I started by streaming to my Xbox but the interface and controls aren't the best, it wouldn't play some files and the sync was sometimes out.
Next moved on to a Patriot media player, no frills but it works quite well, hardwired so it isn't portable. Doesn't play some mkv and wmv files. Very difficult to scroll through movies.
Next tried a WDTV, has built in wireless, runs almost anything, lots of extra features like netflix, facebook, twitter, internet radio, etc. etc.
This is overall a pretty good machine for the money but it has some buggy software. Had to update the firmware about 10 times and the file system has ghost files showing that I can't get rid of.
Finally broke down and spent $190 on a Boxee Box.
http://www.memoryexpress.com/Products/MX31175
Annoying that you need to log in with an email address the first time but beside that it is a great unit. Built in wireless and plays absolutely everything. Has every feature you can imagine, everything that the WDTV has plus way more. You can even watch internet television by accessing the streams from tv network websites. You can surf the web using the coolest remote around, the front is a apple-esque basic remote and the backside has a full qwerty keyboard. Very happy with this unit and you can quickly unplug it and move it to a different room instead of a bulky wired solution.
Right now I'm running a NAS with the Boxee and it is great but you can also connect to your PC or laptop and access media files.
Between netflix, streaming from websites and media files that you get from other sources you can probably get rid of your cable.