I agree with Prague being the best place. Ideal Bachelor party location, plenty of things to do, mainly (and probably only) drinking at low prices. Not to mention some interesting clubs they have there.

I would recommend you some place in the mediterranean, an island like Ibiza, where you can get cheap drinks and fun in San Antonio, the english quarter, go clubbing, chill out in hippie-style during the day, and enjoy beautiful white sandy beaches with the coolest people.