I'd try Ebay and a reputable seller for a hard drive, you can only use MS proprietary ones.
If you like shooters get Gears of War.
If you like JRPG's get Lost Odyssey, Eternal Sonata and Blue Dragon (buy them in that order).
If you like GTA style games pick up Saint's Row cheap. It is really good.
Regardless of what kind of games you like, purchase Bioshock and Mass Effect as they are the two best games of this generation on the high-def consoles.
When they come out this year Fable 2, Banjo Kazooie 3, GeoW2, GTAIV, Ninja Gaiden 2, Infinite Undiscovery and perhaps Too Human and Alan Wake will all be must haves if your remotely interested in the genres.
A list of MS exclusives can be found here:
http://vgchartz.com/forum/thread.php?id=19165
A list of already released great games can be found here:
http://vgchartz.com/forum/thread.php?id=14073
starcraft - Playing Games = FUN, Talking about Games = SERIOUS
