Something that I recently found a need for was adding spell checking to web input forms. With a WordPress installation on another server, I found a spell checker plugin. I wouldn’t say that this plugin was easy to install (the instructions don’t necessarily resolve all the issues with where components are expected to be), but I persevered and it is now working on that site. I plan to implement it for this WordPress installation once I transfer this domain to the new server machine.
Earlier today, I implemented this for the Panda’s Thumb web site, allowing users to spell check their comments in the “preview” of comments.