Free .Net controls
Found a list of free controls for ASP.Net. See them after the jump
Flyout Control (ToolTip Control)
You can use this control as to show tooltip or you can use this control to show flyout or dynamic html while clicking on or
focus on any control. For demo, check the following url.
http://www.obout.com/flyout/flyout.aspx
Panel Control - Strip Control (Can say Tab Control)
This control is really nice to show the different panels, Filmstrip, slide show, shopping show, live quotes, quick news etc.
You can show pictures or different panels into it. really usefull control. just see it working on the following url
http://www.obout.com/show/
SuperButton Control - Image and Text Button
When you require to show image and text in the same button at same time this is the control you are looking for. see it on
following URL.
http://www.obout.com/osb/ex_pressEffected.aspx
Basic Slide Menu - XP Style navigation bar
This is the control which you can see in the left side while nevigating my computer on windows XP machine. it can slide for
the suboption. just look at it. Basic version is free for use
http://www.obout.com/sm3/whatisnew.aspx
Free HTML Editor
FCKEditor is widely used and almost all browser supported control. You can use it as HTML editor in your project.
Excentrics WOrld ( Calendar, Collapsable Panel, Faq, Masked TextBox, Multiline ListBox, Numeric Box, List Transfer, Time Picker)
Excentric world’s control are really useful controls. We are using Calendar control extensively. Other control also can be
used wherever required.
http://www.eworldui.net/default.aspx
MetaBuilders Control ( DIV Combobox,Confirm Button, Dual List Box, Dynamic ListBox, Expanding Buttons, Expanding Panel, Custom File Upload, Linked ListBox control, Scrolling Panel, UpDown controls)
Metabuilders controls are of 1.1 but it can be used in 2.0 as well. These controls are with source code so that you can modify the controls. There are many controls but i have mentioned some of the good one as above)
http://www.metabuilders.com/default.aspx
Free TreeView Controls
SquishyTree control is free control with the source code. You can download it from here below.
http://www.squishyweb.com/ware/products.asp?q=squishytree
Others : http://www.codeplex.com/geniustreeview
Free GridView Control
I haven’t seen it but its free with source code 
.
http://www.codeplex.com/ASPNetRealWorldContr/SourceControl/DownloadSourceCode.aspx?changeSetId=346
http://www.codeplex.com/xgrid
Free Tab Control
A rich Tab web control which provides similar capabilities as the well known windows form tab control
http://www.truecontent.info/topscripts/aspnet-rich-tab.htm
http://www.codeplex.com/GridExtender also contains classic tab control.
Max Input Multiline Text Control, Keep Focus , One Click Button (All ajax control built on top of ajax for asp.net)
http://www.codeplex.com/AjaxControls
ASP.NET Captcha Control
We need some verification for form submit then this control is useful
http://www.codeplex.com/aip
Validator/Validation Controls
http://www.codeplex.com/valever