If you use Twitter's official Mac app on a MacBook Pro Retina you know that it sucks. It's a piece of unreadable blurry crap that makes me want to punch my computer. Thankfully, Tapbots came to the rescue with a gorgeous, Retina-optimised Twitter client: Tweetbot.
Seriously, Mac developers, you need to get up to speed on your Retina versions, because some of your apps are really bad looking now.
Tweetbot, on the other hand, is really pretty and makes Retina shine. Razor sharp. It's an alpha version, so it may boom and bang here and there, but so far it's been solid for me. Get it at [Tapbots]