<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by shanpet:
hi,
i was hoping that someone could give me some advice on choosing a good frequent flyer program. i fly out of st. louis, usually traveling to los angeles or san francisco, about 6 round-trips a year.
i know there are some programs that also give miles when you use your credit cards, and this might be good for me too.
i'm more interested in getting free domestic tickets than i am interested in getting upgrades.
does anyone have any advice for a novice frequent flyer? thanks!</font>
Yup: READ!

There is a wealth of information here on exactly your question. I'm not as knowledgable as some so I'm not including links, but if you do a search you can find almost anything you look for.
For the kind of travel you are doing, if all you care about is free tickets, you might want Southwest (based on your travel mentioned above, it would give you a free ticket the most often, but of course there are drawbacks). If you want to get into the upgrade game and all the promotions then it may work out differently for you (Northwest and United have the best card offers right now, but that changes almost daily).
Hope this gives you at least a start. Search for anything I mentioned above and you will find a ton of relevant information.
Good luck and welcome!