Try askmen.com
I just got asked to be bestman at my best friend's wedding about an hour ago, so I actually just jumped online tonight before heading to bed just to try and find some ideas on that, as well as any other responsibilities I may have!
Good luck, and if you find any good ideas, post 'em for the rest of us that are in that situation (I'll try to do the same)
edit:
By the way, the bachelor party isn't your only responsibility:
http://www.askmen.com/dating/datinga...ting_tips.html
Kinda daunting, eh?