In addition to Max: The Curse of Brotherhood and Halo: Spartan Assault, Microsoft's Games with Gold is getting two more additions this month on the 360 -- Super Street Fighter IV Arcade Edition and Charlie Murder. Starting today, you can grab the latter two games.
As far as the sizes go, Street Fighter is approximately 6.5 GB, and Charlie Murder is around 350 MB. You can find SF here and Charlie here. Remember, you can order them online for free to download later on.