Need a bit more info:
Have you tried it on both sides of the road, taking the road crown out of the picture, does it influence which way the car pulls?
How is the tire pressure - even from side to side, front and back (remember to measure when cold)?
How is the steering wheel, should be perfectly centered when going straight, does it have a noticable tilt when car is centered (have to hold the wheel to keep the car going straight)?
Any pulling when you stomp on the brakes?
If answer is no to all - then it sure sounds like just an alignment issue to me. If alignment is set a little loose (toe neutral or out) then even a low powered car like the Corolla/Prism can be influenced by torque steer (steering influence if you are under acceleration). On some high power FWD cars without LSD and sometimes even with LSD, this can be quite pronounced - ex. try driving a newer Nissan Altima with the 3.5L V6 and and stomp the gas, you'll now exactly what I mean.