Winforms Development:

• MozBar ^[1]
• Krypton Control Kit ^[2] by Component Factory
• DockPanel Suite ^[3]
• "Ribbon" Style Controls ^[4]
• Animation Loading Circle ^[5]
• WinForms Google Earth Plugin Library ^[6]
• SourceGrid grid control ^[7] (formerly devAge)
• Object ListView ^[8], full featured Tree and Grid
• Advanced TreeView ^[9]
• TreeView with GridView ^[10]
• TreeView with Columns ^[11]

Webforms Development:

• AJAX DataGrid ^[12]
• DevExpress Controls Suite ^[13]
• Ajax Control Kit ^[14]
• CKEditor ^[15] (previously known as FckEditor)
• TinyMCE ^[16]
• UserName Availability Control ^[17]
• Webforms Security Kit ^[18]
• Animation Loading Circle ^[19]
• NeatUpload ^[20]
• Various FileUpload Controls ^[21]
• eXcentrics .NET Server Controls ^[22]
• iTextSharp ^[23] (Free PDF On-The-Fly generator)

WPF:

• XamDataGrid ^[24]
• XCeed's WPF DataGrid ^[25]

Graphs and Reporting:

• ZedGraph ^[26]
• Microsoft's new Charting Controls ^[27] (ASP.NET)

Silverlight:

• Silverlight Control Kit ^[28]
• Vectorlight Free Silverlight Controls ^[29]

[1] http://www.codeproject.com/KB/menus/MozBar.aspx
[2] https://github.com/ComponentFactory/Krypton
[3] http://sourceforge.net/projects/dockpanelsuite/
[4] http://www.codeproject.com/Articles/364272/Easily-Add-a-Ribbon-into-a-WinForms-Application-Cs
[5] http://www.codeproject.com/KB/cs/mrg_loadingcircle.aspx
[6] http://code.google.com/p/winforms-geplugin-control-library/
[7] http://www.codeplex.com/sourcegrid/
[8] http://objectlistview.sourceforge.net/cs/index.html
[9] http://www.codeproject.com/KB/tree/treeviewadv.aspx
[10] http://www.codeproject.com/KB/list/treelistview.aspx
[11] http://www.codeproject.com/KB/tree/TreeWithColumns.aspx
[12] http://www.webgrid.com/
[13] http://www.devexpress.com/Products/Free/WebRegistration60/
[14] http://www.asp.net/Ajax/ajaxcontroltoolkit/
[15] http://ckeditor.com/
[16] http://tinymce.moxiecode.com/
[17] http://www.codeplex.com/UsernameAvailability
[18] http://www.codeproject.com/KB/web-security/WebPageSecurity_v2.aspx
[19] http://www.codeproject.com/KB/cs/mrg_loadingcircle.aspx
[20] http://neatupload.codeplex.com/
[21] http://remy.supertext.ch/2008/01/file-upload-with-aspnet/
[22] http://www.eworldui.net/
[23] http://sourceforge.net/projects/itextsharp/
[24] http://www.infragistics.com/dotnet/netadvantage/wpf/xamdatagrid.aspx#Overview
[25] http://xceed.com/Grid_WPF_Intro.html
[26] http://sourceforge.net/projects/zedgraph/
[27] http://weblogs.asp.net/scottgu/archive/2008/11/24/new-asp-net-charting-control-lt-asp-chart-runat-quot-server-quot-gt.aspx
[28] http://www.codeplex.com/Silverlight
[29] http://www.vectorlight.net/

Check also the AjaxControlToolkit ^[1], they are very customizable ASP.NET AJAX extenders and controls.

[1] http://ajaxcontroltoolkit.codeplex.com/

There are a lot of free controls available, but by long, hard experience I stay away from them (as well as commercial control libraries) as much as possible. First, there's the learning curve -- and then the almost inevitable bugs or inexplicable behaviors. Deployment can also be a pain.

If I can't find the control I need in the .Net standard controls, I'll first think about building a user control (or searching the web for something similar that includes source code). If I focus on a user control or source-included control, I then try to evaluate the cost (time) of implementing it -- and compare that to the cost/time of a shareware or commercial control. And, finally, try to evaluate whether the app really needs this whiz-bang thingie or not.

The answer is usually 'not'.

ZedGraph ^[1] is an awesome graphing library a coworker of mine used on a project recently. They have a lot of examples and excellent documentation, too. It's free (LGPL).

[1] http://sourceforge.net/projects/zedgraph/

The new charting controls from MS.

http://weblogs.asp.net/scottgu/archive/2008/11/24/new-asp-net-charting-control-lt-asp-chart-runat-quot-server-quot-gt.aspx

DevExpress ^[1] has 60 freely available controls, and a large set of commercially available controls. We use them in all our projects and I like them for they flexibility and beauty.

[1] http://www.devexpress.com/Products/Free/WebRegistration60/

https://github.com/ComponentFactory/Krypton - The Krypton Toolkit is not only a very powerful and well built component library, it is free for use and well supported by the developer. If you try it and like it, there are options for purchasing the source code (for a very reasonable price) and for buying extended feature sets in additional libraries.

I'm not sure why, but no one has mentioned Ext.NET ^[1] nor ExtAspNet ^[2].

Both of these wrap ExtJS ^[3] for ASP.NET. Ext.NET ^[4] has the most features. ExtAspNet ^[5] is easier to get started with.

[1] http://www.ext.net/
[2] http://extaspnet.codeplex.com/
[3] http://www.sencha.com/products/extjs/
[4] http://www.ext.net/
[5] http://extaspnet.codeplex.com/

These WinForm controls are discussed further on my open-source website here ^[1]; I have published in-depth articles on several of them as well.

• ChameleonRichTextBox ^[2] enhances a RichTextBox with language-specific syntax highlighting, keyword completion (a modest Intellisense), search-and-replace capability, macro support, plus some additional keyboard formatting controls.
• ExtendedDataGridView ^[3] extends a DataGridView with filtering, searching, sizing, masking, formatting, and export capabilities.
• FileMask ^[4] filters a directory by specifying one--or more--file masks displaying both the list of matching files and a count of matched files; it additionally allows customizing this generic control with additional arbitrary criteria.
• MultiConnectionStringManager ^[5] lets you manipulate and test a set of database connection strings and associated details for SQL Server, Oracle, MySql, plus any ODBC data source. It provides interactive handling of database credentials, giving you everything you need to control how users input usernames and passwords, select servers, and choose connection types.
• QueryPicker ^[6] builds meta-queries from templates, dynamically generating a set of input fields for the place holders within a meta-query template, then letting the user enter values in any or all fields, and finally returning a finished meta-query. Supports SQL Server, Oracle, and MySql.
• SqlEditor ^[7] is an "editor in a box", composed of a ChameleonRichTextBox customized to recognize SQL dialects, an ExtendedDataGridView, a QueryPicker, a MultiConnectionStringManager, and more.

[1] http://cleancode.sourceforge.net/wwwdoc/software.html#UserControls
[2] http://cleancode.sourceforge.net/api/csharp/html/T_CleanCode_ChameleonRichTextBoxControls_ChameleonRichTextBox.htm
[3] http://cleancode.sourceforge.net/api/csharp/html/T_CleanCode_DataGridViewControls_ExtendedDataGridView.htm
[4] http://cleancode.sourceforge.net/api/csharp/html/T_CleanCode_GeneralComponents_Controls_FileMask.htm
[5] http://cleancode.sourceforge.net/api/csharp/html/T_CleanCode_DatabaseControls_MultiConnectionStringManager.htm
[6] http://cleancode.sourceforge.net/api/csharp/html/T_CleanCode_DatabaseControls_QueryPicker.htm
[7] http://cleancode.sourceforge.net/api/csharp/html/T_CleanCode_SqlEditorControls_SqlEditor.htm

Uploading large files with ASP.NET:

NeatUpload ^[1] - Looks like a pretty cool Open Source Component. The Progress Bar is in an IFrame and seems to do its job, but the update steps are not very fine grained. Also supports Mono!

More at http://remy.supertext.ch/2008/01/file-upload-with-aspnet/

[1] http://www.brettle.com/neatupload

There's a great Office 2007 style ribbon in CodeProject:

http://www.codeproject.com/KB/toolbars/WinFormsRibbon.aspx

What about this one? This a loading animation which mimic pretty well the FireFox/IE animation.

http://www.codeproject.com/KB/cs/mrg_loadingcircle.aspx

A couple of WPF datagrids

• Infragistics' xamDataGrid ^[1]
• Xceed's DataGrid Express Edition ^[2]

I've been using the xamDataGrid mostly.

[1] http://www.infragistics.com/dotnet/netadvantage/wpf/xamdatagrid.aspx#Overview
[2] http://xceed.com/Grid_WPF_Intro.html

There are some great free silverlight controls ^[1] here.

[1] http://www.vectorlight.net

Rich text/html editor for websites:

http://www.fckeditor.net/

Not a visual control, but if you need anything with PDFs, iText# ^[1] is extremely powerful, and the accompanying book iText In Action is a pleasure to read (colleagues have used it without the book productively too though).

(I used the PdfStamper to manage form inputting via FDF for forms scanned in Acrobat Pro)

[1] http://itextsharp.sourceforge.net/

winforms-geplugin-control-library.

Open source controls to work with the Google Earth Plug-in Api from managed code...mine

http://code.google.com/p/winforms-geplugin-control-library/

I like the idea behind this control:

• Username Availability Validator ^[1]

[1] http://www.codeplex.com/UsernameAvailability

Free Custom Web Controls, E-World UI, very useful : http://www.eworldui.net/

The docking library for .Net Windows Forms development which mimics Visual Studio .Net. : DockPanel Suite ^[1]

[1] https://sourceforge.net/projects/dockpanelsuite/

Great library to ensure https security for pages/folders of an asp.net website, configurable via the web.config file:

http://www.codeproject.com/KB/web-security/WebPageSecurity_v2.aspx

There is also visual web gui. I used it in a previous workplace. A word of caution: there are some bugs, some hacks, rough edges, and corner cases. But these are pretty minor considering the breadth of the project - which is to provide asp.net as winforms programming.

Here are 2 more vendors with some freebies:

1. Free .NET Components for WinForms, WPF and Silverlight - www.viblend.com

2. Free .NET Components for ASP .NET, Silverlight and WinForms - www.devexpress.com