ieSpell is a free Internet Explorer browser extension that spell-checks text input boxes on a Web page. It should come in particularly handy for users who do a lot of Web-based text entry (e.g., Web mail, forums, blogs, diaries). Even if your Web application already includes spell-checking functionality, this utility is faster than a server-side solution. Plus, you get to store and use your personal word list across all your applications instead of maintaining separate ones on each application.
Note: The program installs as a new button in the IE toolbar (as well as a new menu item under Tools). After filling in a form, click the ieSpell button and it pops up a dialog similar to the Microsoft Word spell check.