Having just bought a 360, I am keen to find out what peoples absolute must have games are (that are out currently and that you have played).  So give me your top 5 (in order of greatness).  I have bought GoW, Perfect Dark Zero and Rainbow Six Vegas (purely because of the co-op split screen), although quite keen to find out whats really awesome.

Also, what may I have missed from the launch of the 360 that would be a must buy in your opinion?

Cheers

The Orange Box
Halo 3
F.E.A.R
Bioshock
Forza 2
Call of Duty 4
Clive Barkers Jericho.
12Months Live subscription

My Top 5:

Bomberman Live!
Hours and hours of fun.

Gears of War
Possibly the best Single Player game I have ever played.

Call of Duty 4
Easily as aesthetically pleasing as GoW, if not more so.
Ive been loving the MP so far.

Forza Motorsport 2
Ive become a little bored with the Single Player now but I still love tuning cars and racing them online.

Colin McRae DIRT
More arcady than Forza but much more "pick up and play"

I have PGR4 and PES2008 sitting on the side waiting to be played but COD4 is taking all of my attention atm.

If you can get them pre-owned then Id also tip my hat to:
The Orange Box - excellent value
Halo3 - for the online play
Rainbow Six Vegas - generally good fun
TopSpin2 - single player is a lot of fun
G.R.A.W / G.R.A.W2 - One or the other though imo
TigerWoods 07/08 - Again one or the other

Making this list has made me realise just how many games I have played and although I enjoyed them at the time, they didnt leave a lasting memory with me :s

PGR4 fo sure

elder scrolls: Oblivion

its good for quite a few hours of game play

bioshock - best FPS on the 360 so far bar none, imo. Graphics & Variety heads and shoulders above others

Assassins Creed is a great game.