Tango or Fring would be the best current options i think...at least until the Google Talk (video function) is released ...it was shown at Google I/O this week but i dont know the push date for it..
It already runs on anything 2.3 (.zip i have) and it was awesome on my incredible but it wont run on 2.2
if a dev wants to take this up let me know i can send the /zip w/ .apk