PingChat is pretty good. But then I'm on a crusade to get people to go back to using IM services like Google Talk, Yahoo IM, etc...
Personally I use Trillian, and you can file transfer via Google Talk with it. There are other all-in-one clients out there too. IM+ and BeeJive are also reputed to be pretty good (which you may be familiar with as they're available for BB). As well there are some free ones out there, but I've used those and they're battery hogs since they don't use c2dm push, and aren't as well engineered.
And sometime soon (crossing fingers) google is supposed to come out with a new version of their gtalk app which will provide access to features the current client is missing... like group chat, file transfer etc.. It's weird that the current gtalk app was designed and released without those features.