Qik - works great on CM6 but it force closes on CM7. Video quality is good and audio is ok good enough to do the job
Tango - works great on CM7 with a mod where you can use front and back cameras. But on CM6 it only detects the back camera. Video quality is good but audio not so good
Fring - works on CM7 with out any mods but the video and audio quality is not so good. On CM6 it only detects the back camera.
Oovoo - is the new kid on the block working great both audio and video on CM6. I didn't test it on CM7 so if someone does let me know this app and Qik is the reason why I went back to CM6 from CM7.