UltimateSpell is a server control to add spell checking functionality into your ASP.NET web
forms, web services, and Windows Forms applications.
Spell As You Type - Underline spelling errors as you type in any editable control on your web page.
Auto Correct - Automatically correct your spelling errors as you type.
Auto Find - Automatically find and spell check all editable controls, or specify a comma separated list of control ids to spell check.
Look Up Meaning - Look up the meaning of a suggested word in an online dictionary.
Lots of Dictionaries - Use 34 dictionaries available on our website, or use your own.
Custom Dictionaries - Add words to your custom dictionaries, and cache them as regular dictionaries.
Spelling Options - Lots of options to change the behavior of the spell checking engine either on the server-side, or on the client-side.
AJAX Enabled - Spell check very long text by sending small blocks of text to server using AJAX techniques without refreshing the page.
Cache Dictionary - Automatically cache dictionaries for fast spell checking.
Check Selection - Select a piece of text and spell check only the selected area.
Language - Display different wordings in spell check dialog box based on your language.
Server-Side API - Use the spell checking engine from inside ASP.NET web, web service or Windows .NET applications.
Client-Side API - Open the spell check dialog box from any client-side action.
Supports Windows Forms - Use the Windows Forms samples in C# and VB with full features and user interface.
UltimateEditor & UltimateSearch - Built-in integration with our ASP.NET editor and search components.
the download link 1 is for .NET 1.x,the 2 for .NET 2.0,the 3 for .NET 3.5.