You can pretty much use any regular bluetooth headset, you just have to pair it with the PS3. Motorola sells the one that we use and it was only $19.99. There are only a couple that don't work, but they tend to be more expensive
Otherwise, if you have any singing games, like Karaoke Revolution or Rockband that use USB mics, they work as well. The only thing is that you'll have to rig it up over your shoulder so that everyone can hear you during game play.