The Browing BPS is a great pump action for a left-handed shooter... It has bottom-ejection and a tang safety, so it works the same no matter how you shoot. Ithaca's model 37 also has bottom-ejection, and you are able to order it with a left-hand safety. Remington has the model 870 Express pump with a true southpaw action, but the quality doesn't really compare to the Browning or Ithaca, although it is still a good value. All three are available fairly cheap new-in-box, but if you are willing to spend a bit more, the Benelli M1 and Remington 11-87 are very nice auto-loaders. The links to all five models are listed below.

As for the used Winchester Super X2, that would also be an excellent choice if in good condition. Good luck!

http://www.browning.com/products/cat...asp?value=011B
http://www.ithacagun.com/products/catalog/
http://www.remington.com/firearms/le...d/870EXPLH.HTM
http://www.benelliusa.com/firearms/lefthand.tpl
http://www.remington.com/firearms/le...1187PRLCLH.HTM