Resistance: Fall of Man is a solid game, especially considering it was a launch title.
Resistance 2 was good as well, but kind of regressed a little bit, IMO.
It's a pretty average franchise, but maybe Resistance 3 can turn it around.
inFamous is a shooter of sorts. Basically all your guns and grenades are electricity based. It's open world and it's pretty fun. I highly recommend it.
Killzone 2 is fun as well. It probably has the most realistic sounding weapons and explosions. Killzone 3 is releasing next week though. It's rumored to have a short campaign, but if you like MP that could make it worth your money.