Recently, lifehacker had a poll of the five best twitter clients [link] most of these are cross-platform and the only ones I actually use are Tweetie (mac) and DestroyTwitter (pc). There's also a new mac twitter client on the scene called Twitt [link]

Twitt still needs work but so far, I like it better than Bluebird, I'm also really diggin' the Bai 白 theme [link]

So yea, I wanna know what your favorite twitter client is on your mac/pc/mobile... here's some to get you started...

Tweetdeck
DestroyTwitter
Twhirl
Seesmic
Eventbox

Tweetie
Twitt
Twitterrific
Bluebird
Pwitter
Beak

Twitterfon now known as Echofon, it has a really nice native mac twitter client too! check it out: [link]
Birdfeed
etc

ooo also, leave your twitter pages if I don't already follow you