Web 2.0 software wishlist – party and holiday planning

Ok, Lifehacker. I throw down a challenge.

I would like a web tool that helps me organise a night out where I need to check everyone’s availability, take suggestions for what to do and (democratically) or otherwise choose the best course of action for a group. I know about evite and mypunchbowl, but when you don’t know what the date is going to be, how do you avoid those reply-to-all-fests?

I would also like a piece of software to help me organise holidays. Gauge requirements, collect details where required, check dates, budget, etc.

If these don’t exist, would someone start something that does them quick and let me know? Rather than trying for another social networking site or social bookmarking site… etc? I’ll probably even pay to use one if there’s a decent, not-too-expensive one out there.