Some Sport Chalets offer free monthly intro classes that'll get you in the water and blowing bubbles. It's a good way to check it out and you won't need anything beyond a swim suit and a towel. It's a good place to start asking questions.
If you decide on getting certified, PADI is the most internationally recognized certifying body, which is makes it easier if want to dive on vacation. There is also NAUI, SSI. PDIC, NASE, SDI.... a few more. I'd stick to either PADI, Naui or SSI.
You'll need at least a mask, snorkel and fins (you may already have that if you snorkel) for your first cert (open water diver) . Everything else can be rented.
Sports Chalet is a good place to get certified, but not necessarily the best. I'd visit a few shops, ask a few question ands try to meet the instructors. Like most guys here try to support their local bike shop (LBS), I try to support the local Scuba shop. Just go w/ the shop/instructor that yo feel comfortable with.
You can save a lot of money on additional equipment and study material by shopping online, ebay, craigslist, scuba.com, etc. However, if you buy anything technical, like a BC, computer, tanks, octopus, regulators, etc., be sure that you have it inspected at your local shop (do it annually, minimum) before you take it in the water.
I belong to an online adventure group SCOA and they occasionally have discounted classes.
http://www.scoaoutdoors.com/calendar/12385009/?from=list&offset=0
Hope this gets you started.