I have a Left Handed CZ 452 American .22 (bolt action), and a Left Handed Stag 3L AR-15. Both are excellent, and I like to support companies that make left handed firearms.
For handguns, I've tried/owned a buch, and I like the new HK's the best. The P30 is almost completely ambidextrous. The HK45 comes with the safety set up for right handed use, but you can get a left handed or ambi safety installed - at the factory only unfortunately.
Glocks, XD's, Sigs, and most handguns without manual safeties are fine for lefties. You just get used to hitting the mag release with your index finger, as well as the slide release. It's better to "sling shot" the slide anyway.