Messages (barely) supports iMessage, to the point where I use it to talk to two people and only because they're not reachable otherwise. Big fan of how Messages decides to lose history seemingly at random and only display fragments of previous conversations. Bigger fan of how the conversations it decides to show at the bottom of the log are from weeks prior.
I use Adium for everything else because I know it works.
You may now use 'j' and 'k' on your keyboard device to flip through the themes. There is also now a gallery link. The theme I'm using is Tomorrow Night, from https://github.com/chriskempson/tomorrow-theme. Enjoy.