The three new maps are all free and available now from id Software's website. The maps are a mixed bunch: Railed is designed for tournament play and is set in an abandoned Strogg facility, with the emphasis on close-quarters combat; Tremors is a Capture The Flag map, built within an enormous twisting underground cavern; and Campgrounds Redux is a remake of the classic Quake III Arena Deathmatch map.
Expect more in the way of new maps in the New Year. These new maps are for the PC version of the game. There is currently no information on whether they will be made available for the Xbox 360 version.