Don't forget Fallout : New Vegas
You can get it cheaper then buying all the Fallout expansions.
I've currently clocked up around 80hrs on Vegas and have only visited about 50% of the places, so easy to enjoy creating weapons, ammo and grub and wonder around aimlessly.
Better (and seems much bigger) game then Fallout 3 imo.
EDIT: Just realized you have the GOTY version. It's worth moving onto them now as you'd get xp quicker.