Pelicans are what I am using. If you have a really expensive slr camera, you can buy a Pelican case that has the cut-out foam interior so you can make it fit perfectly. I have one for an audio field recorder I own. Cost about $30.
I carry my compact camera in a small clear pelican case. Works great.
I recently noticed that Olympus sells some of their underwater camera housings very cheaply on ebay. For an upcoming trip to Panama, I bought a case waterproof to 140 feet for about $40 and a used camera to fit it for even less.
If you are in the market for a camera, both Olympus and Pentax now have some very nice and not too expensive waterproof/dustproof models that would be great compact caving cameras. I have a Pentax Optio W20 that is waterproof to 5 feet. Good enough that it can get wet or dropped in a stream and survive.
I use a small Pelican case, model 1010. I really abuse it. It stays cliped to the outside of my pack so I can get the camera quicker. It is fast to open and close. I take lots more pictures this way. I use it also for canoeing and rafting. I also like the clear door so you can see what is inside.