The new Roku XDS looks like a pretty compelling little device for $99. It plays content from a variety of streaming sources. Both paid and free content is available. It also should be capable of playing some video files off a USB drive in November following a software update. Unfortunately they forgot to build in support for AVI files, which seem to be very common at the moment.
In comparison, the newly redesigned Apple TV only plays content from two networks currently (Fox and ABC), and each TV show costs 99 cents. I’d be okay with paying 99 cents for TV shows, but if there are only two networks available then I’m still going to end up having a cable subscription. So I don’t really understand the point.