little big planet killzone 2, and motorstorm pacific rift , if u want one of those to be replaced i can recommend u uncharted

I'd grab Uncharted, Folklore, and GT5P.

MGS4--TPS/Stealth/Action
Uncharted--TPS/Action
Burnout: Paradise--Racing

MGS4
Uncharted
LBP

Uncharted(best game this generation so far in my opinion)
Street Fighter IV(everyone who plays fighting games seems to like it)
Burnout Paradise(can be had for pretty cheap, maybe enable you to get a 4th game)
Killzone 2(potential to be an amazing FPS you wouldnt want to miss out on)

uncharted

KZ2/MGS4

burnout or motorstorm PR(if you want split screen then definitely MS:PR)

Shooter - Resistance 2:
Since you only have enough money for 3 games Id expect you'd want some great replay value.R2 has the best online(imo)for any ps3 game and will last ages.

Racing - Motorstorm:Pacific Rift:
Vastly superior to the first,And an amazing racing game all around.Has really great online as well.

TPS - Uncharted:
It has an amazingly fun SP that you will play through more than once.The story is phenominal and interesting.

How can you say you only have enough money for 3 games when every game doesn't have the same price tag?

MGS4
LBP
Killzone 2

(Then after a while Uncharted, GT5 Prolouge, Motorstorm Pacific.)

Over all, Oblivion GOTY is a must. Racing wise, Burnout is very good but because its an open city has the problem of taking a wrong turn and bang you lose. For that very reason i prefer GRID. The last I would go for Farcry 2, although a little vast and spawning issues its still got me hooked