I know I'm not the only person looking forward to this game. Fallout 3 was amazing and this game appears to be following suit. I just came across some scans from two articles about F:NV in a Playstation and XBox magazine. This post is specifically related to the ones featuring guns.
First
I'm thinking maybe XM177E2 or Model 733
Second
Looks like a Browning Hi-Power
Third
Possibly just a generic cowboy gun, Single Action Army likely.