I got an Apple TV back in April and have been very happy with it. Movies, music, and purchased TV series all stream from my laptop and/or the cloud and I can watch anythhing Netflix has to offer as well.
Granted, I do a lot of my TV viewing after shows air, so I'm usually just mirroring HBO from my iPad or the network website from my laptop on to the TV. So far, it's worked pretty well.
I've heard good things about Roku, but I have no personal experience with it myself.