I'm a big fan of ChiefDelphi.com forums and I think you can help clean up the interface by have sub categories for each of your categories,
For example,
Electronics : Microcontrollers , Power , Sensors
Mechanical : CAD , Animation , Motors/Gearboxes , FEM
Misc : Robot Competitions , Forum Suggestions, Q&A
Having RSS feeds for each category might also improve the forum experience,
Here's an example,
http://www.chiefdelphi.com/forums/index.php?Feel free to post any sub-categories you have,