I've recently switched to Adium and managed to consolidate all of my different IM accounts and contacts (MSN, GoogleTalk, AIM) under a single client with the same "look and feel". This alone makes this piece of software a blessing.
Now if only some sort of basic skype support was added.
This is possibly the most popular request in Adium's issue tracker -- the infamous ticket #247 if you want to check it out.