Here are a few sites. Please post any others you have found especially useful. Thanks!
Carol's Corner Office: Lots of tips and tricks for MS Office here. Check out her Free Word Bytes Newsletter, as well as her subscription premium newsletter and her books.
Word for PC, Tips, Tricks, Troubleshooting: Part of the MPV website.
Word Shortcuts: A page from the above MPV site.
Useful MS Word links on Microsoft's website: MPV has compiled a handy list of links.
Word Tips by Allan Wyatt: A weekly email newsletter full of tips. The writer has also published a book of tips.