That said, there's a good next choice: Buy a camera, then buy an underwater housing for it. Here you have quite a few choices, really depending on your budget and the type of camera you want. You could, for instance, get a Canon G3 Powershot ($700; www.canon.com), a very good four-megapixel camera with a 4:1 zoom lens. For dry-land use, it's just the ticket. Then, for aquatic adventures, stick it inside an Ikelite 6143 housing ($650; www.ikelite.com), designed specifically for the G3. OK, I admit the whole setup is pretty pricey, but it's also one that's going to work extremely well. Ikelite has been making housings for decades and knows its stuff.
Of course, you can spend less. You could, for instance, get an Ewa-Marine housing for that same G3, and spend only $150 for it. The difference is that the Ewa-Marine housing is essentially a high-end plastic bag (it's made like the roll-top bags kayakers use) with a hard plastic lens cover, while the Ikelite is all hard plastic. Or you can get an Ewa-Marine housing (www.ewa-marine.de) for a lesser but still-capable camera such as the Olympus C3000, a three-megapixel camera (no longer made, but available by the score from eBay for bid prices around $250).