How bad does it pull? Violently, or just barely, or somewhere between. My guesses are: (not in any certain order)
1) Old brake fluid/air in the lines
Bleed brakes with a quality brake fluid - push out enough fluid through each line until you see the new fluid coming out.
2) Brake pads
Check and replace pads as necessary (do rears as well)
3) Some how the brake bias (the pressure that is divided between front/rear and left/right) is screwed up.
Could be the master brake cylinder or the brake bias valve - take to a repair facility.