The most prevalent HD sources are gaming consoles. The PlayStation 3 and Xbox 360 both offer 1080p output, and many games take advantage of this (though most are 720p).
A less common route, but perhaps with an even more vocal fanbase, is the home theater PC (HTPC): a computer designed to work in a living room/theater. Computers can easily create 1080p (and much more), and do more than just gaming and movie playback.
So the question is, what do you use for HD gaming? Do you have a console, but don't have it
Are you a die-hard PC gamer who has transitioned your hobby to the big screen?
I'm curious to hear your thoughts in the comments below.