I used to flip with a pricecheck fc. I don't remember the name though. It ended up with me having some specific items which I'd flip on several accounts for ge slots. I've heard about this site, but never bothered to try it because most, if not all, prices can easily be checked on forums.
If you have cash, I'd just start with partyhats. You can either join a pc clan/fc or look on forums. Alternatively, merchz.com