A boxing game looking to beat all other boxing games in realism, Fight Night Round 3 has a demo up on the Xbox Live Marketplace.
The game looks pretty real, and if my router was working, I could tell you how big the demo is. No doubt it is over a couple hundred megs, so get ready to sit and wait again.
Update: 486.44 MB for this demo. I am downloading it now that my router is up and working.
Note: Not available in Japan or Korea