...so I figure I have a big catalogue of games that I´ve missed...I´m planning to get:

-Kameo

-Gears of War

-Bioshock

-Halo 3

-Mass Effect

-Lost Odyssey

-Ninja Gaiden 2

-GTA 4

Any other suggestions/opinions would be welcome.Thanks.

Oh, and I can expect Fable 2 and Banjo 3 this year, right?

You should expect those two this year, Banjo is probably coming out in november,and it is not a racer

Assassins Creed if you dont have that on another system youll defenitly want Gears 2 when it comes out

Right on the money and welcome to the club!

You might want to consider the following as well:

Eternal Sonata
Crackdown
Dead Rising
Viva Pinata
Forza 2 or PGR4 (if you like simulation racing)

This list is full of win.

Give Crackdown a shot.  MrStickBall has an excellent list of budget titles stickied in the Microsoft forums which he updates regularly. 

Eternal Sonata

...and do you have a PS3?

Cause CoD4 is great, and DMC4/The Darkness are vastly under-rated, and I hear the PS3 version of F.E.A.R. sucks, so you might wanna check that out.

Great list, JGarret. Only games there that I don't own are Kameo and LO. As other have stated, Forza 2 if you like racing, you can get it cheap. Blue Dragon and Eternal Sonata if RPGs are your thing.

Oh, I forgot some:

Ghost Recon Advanced Warfighter

and

Overlord

Both of those games are great.

I suggest skipping Gears of War for either one of them...and maybe Kameo too.

Eternal Sonata
Dead Rising (x2 )
Left 4 Dead when it comes out, but only if you're getting Live.

You should give Condemned 2 a try, its quite a fun game. Not perfect but it gives a nice mix of fighting/shooting and its definately different from the other games on your list. You could also get the first one at the same time, its better IMO and it should be cheaper too.