As others have suggested, check the control arm bushings, but they won't usually cause a constant pull. They'll cause brake pull and bump-steer, but not a constant pull.
Have you checked tire pressure? Possible tire pull?
Do you have an alignment printout showing you where everything is and where it should be? If so, are there variations in the different printouts you've gotten from the shop?
There is a local tire shop that advertises free two-wheel alignments with a tire purchase. Their big promotion is that they don't do any front end work, so there's no up-selling. You'd be amazed at the cars they've aligned. I had a Saturn that came in two days after one of their alignments with a broken lower ball joint. Some "alignment guys" wouldn't know a bad part if it fell apart on its way into the shop.
Eric