Achievement: The "I like sex scenes" achievement... acquired after going through Mass Effect 4 times to see all 5 sex scenes (there's 5 possibilities). This would be a downloadable one, so 250 points.
Dashboard Feature: How about syncing to itunes? That would be nice. Or maybe allowing a keyboard and mouse to be used on games that support it? Or using AIM instead of MSN Messenger for the IM? Or how about supporting logins from multiple 360's without having to recover your gamertag (so I can log in at one 360, download stuff, then log in on another and have access to the same stuff, as long as the two aren't connected simultaneously)?
Game: PGR4 please, should you deign me worthy of a prize.