Everyone has given you some pretty good advice here about fittings so I'll throw in my two cents. If you plan on doing some serious riding, don't skimp on the fitting or the price because you will get what you pay for. I ride between 5 to 6,000+ miles a year and a LBS initial fitting just isn't going to cut it when you put that much time in the saddle. Personally, I opted for a Retul fitting and it was the best $250.00 I ever spent on cycling, other than my bike. I don't race or do tri's but I do a lot of hard riding and I have not been dissatisfied with the fitting process. Find a system that will meet your riding needs and if your riding needs change, find a new system that will work for you.

Edit: I would also advise that you check out all the different fitting types and learn as much as you can about them. Don't just leave it to the guy behind the counter to tell you what sounds good. Also, find out as much as you can about the fitter. Find out how many fittings he has done and if he is the only one in the shop that does the fittings. I realize that depending on where you live that some fitting systems are not available, but the better prepared you are when you go for your fit, the less chance there will be in getting ripped off and get a poor fit.