A waterproof camera is a great idea for travelling, especially if you're spending lots of time on the beach or by water. You have two choices really: an underwater camera, or a normal camera with an underwater housing. The latter will allow you to get hold of a better quality camera from the start, but will be pricier - and normally bigger too.
If you're after an underwater camera, the Canon D10 is our current pick:
But remember it's a compact, so you ewon't get great quality in low light. For that you'll need a DSLR.
Our quality recommendation would be the Olympus E-620 (or an older E-520) with their optional underwarer housings. Bigger, priceir, but better quality.