Give your applications the ability to carry out spelling checks against user input or database fields.
 How to Spell Check Web Page Input
 How to add as-you-type spell checking to .NET Windows Forms applications

ASP.Net Spelling and Spell Checking Components by Telerik Inc.

RadControls for ASP.NET AJAX 2008 Q2 SP3

RadControls for ASP.NET is a professional toolset designed to help ASP.NET developers deliver feature-rich, standards-compliant and cross-browser compatible Web applications on budget and on time. Easy to use and customize, the controls provide full support for AJAX and Visual Studio 2005, seamlessly integrate in MOSS and WSS and are fully standards compliant (WAI-A, WCAG 1.0, XHTML 1.1).

Telerik Premium Collection for .NET Q3 2008

This comprehensive toolset allows you to rapidly build commercial-grade interfaces for web and desktop applications and meet the diverse functional, design and usability requirements of your clients. Over 40 ASP.NET AJAX components, robust WinForms Controls with WPF-like visual effects, and a flexible reporting engine are there to help you quickly create .NET applications on budget and on time.

ASP.Net Spelling and Spell Checking Components by Aspose Pty Ltd

Aspose.Spell for .NET V1.9.1

Aspose.Spell is one of the .NET components offered by Aspose that supports multilingual spell checking in 22 different languages. The list of languages include: Danish(DK), Dutch(NL), English(US), English(UK), English(NZ), English(AU), Germany(DE), French(FR), Italian(IT), Polish(PL), Portuguese(PT), Russian(RU), Spanish(ES), Swedish(SE). Afrikaans(ZA), Catalan(ES), Faroese(FO), Galician(ES), Greek(GR), Irish(IE), Latin(LA), Norwegian(NO).

ASP.Net Spelling and Spell Checking Components by Keyoti

RapidSpell Desktop.NET 4.0

Integrate spell checking functionality into .NET Windows applications. Add spell checking value to any textual application (email, word processor etc) with a couple of lines of code. RapidSpell Desktop can also be used in non GUI contexts using it's spell checking API. Written for dotNET in C#, RapidSpell uses combined and separate 140,000 word U.S. & U.K. dictionaries (and user dictionary), multi-threaded GUI and a powerful suggestion engine.

RapidSpell Web.NET 3.5.1

RapidSpell Web provides a spelling component to add spell check functionality to your web applications, by simply adding the Web Control to an aspx page (Web Form) or directly accessing the classes in a code behind page. There are no programming skills required to use RapidSpell Web, because of it's strong visual designer (VS) design time support, making this ASP.NET spell checker control accessible to ASPNET page designers.

StudioSpell V3.0

StudioSpell is an easy to use speller Add-In for Microsoft Visual Studiotm .NET (2002 and 2003), providing a user friendly tool for checking web-page Html and strings in source code - StudioSpell analyzes only the text that could appear in-front of a user.

ASP.Net Spelling and Spell Checking Components by ASP Spell Check

ASPSpellCheck V2.6

ASPSpellCheck provides international spellchecking for your ASP applications. It is suitable for use with W3C HTML and XHTML applications, and has a good degree of accessibility. With no ActiveX controls, Database or DLLs to install, you can be up and running in minutes. ASPSpellCheck even be used on virtual/shared hosting.

ASP.Net Spelling and Spell Checking Components by Tachyon Labs

SharpSpell 3.0.1 -  SharpSpell 3.0 is the most technologically advanced ASP.NET spell checker and Windows.Forms spell checker component available on the market today. Automatically attach AJAX real time wavy underline spell checking to any TEXTAREA element (ASP.NET) on your site!