I like either IM+ or Beejive.
Both are really good apps, Beejive doesn't have Skype, but I use the official skype app most of the time anyways.
(IM+ works on the iPad too though, so thats a big plus factor).
@appleweek: I used PingChat for a while, but it never caught on with my group of friends, everyone is using Kik now, so I use that more often and its really cool! Much more like BBM (I have a blackberry and have Kik synced to my blackberry and ipod touch to chat with my iPhone and Android user friends).