One of applications I missed for Mac when I switched was a good Bittorrent client. I've tried all of them and all of them seem fairly mediocre, but this morning I found Transmission which is awesome. It's a native Mac OS X application for 10.3.9 and up. It looks like it's in beta, but it's solid. The icon could use a little work, but don't let it deter you from trying it. The only thing it lacks is an upload ratio, but I think they're adding one soon. I've added a screenshot, because if you're like me, a screenshot tells you a lot about the program.