Good Ideas for Service Related Site?
 

I'm considering several different kinds of sites to set up and would like some feedback on what you think is the best of the bunch, or suggest something else. Here's several I'm considering:

Auction site
Freelance job posting site
Dating/Personals site
Price search--for lowest price
Portal--targetted portal
Classified Ads site

Anyone think any of these a good idea? Anyone had success with any of them? Can anyone point me to some relevant data on how well these kinds of services are doing or are expexted to do in the near future?

TIA