Pretty self explanatory, and I think the makers of the plugins deserve some recognition too.
I'll start:
1. BOB - sherkaner - absolutely essential tool for the site, makes games much more enjoyable by presenting all the information in a simple format - plus the connectivity indicator is a wonderful backup for complex maps such as forbidden city and waterlo.
2. Chatglove - foxglove - really underrated tool for team games that allows you to keep everything on one screen.
3. Clickable Maps - not just for freestyle, a handy application to reduce drop down errors (which I've made too many of).
4. Maprank - ChipV - not an essential tool but really cool, and allows you to determine strengths and weaknesses for team play and clan wars.
5. Watch this Game - Dako - really nice tool for clan war management and tournament management. Makes it easy to check up on progress without digging through old threads.