That was basically my first question on aardvark.
I know just of 3 good options:
As Alexander said, Google Talk. You have to configure it using another Jabber Client such as Psy, on linux. The keywords here are gateway and transport. It's not easy, but this will give you the best results.
As you've suggested, a web client. There are many clients out there, nimbuzz is the best for smartphones nowadays; e-buddy has the simplest interface and the less bugs, but also the less features; and find imo.imm even better than meebo but meebo is the only one with good chat history.
IM-history for a paid solution. This will even send your skype chat to GTalk, something you can't do with the first option alone. At least I don't know of any jabber gateway for Skype.
For the first option, which is what I use, I would quote some links from my vark's answer, to give you an idea it won't be easy to configure. But it's too big. Granted, once set up, you'll have all working even inside Gmail.