To take along on a conoeing trip, just in case I fall in! (ie not for underwater photography but able to resist a quick dunk)
Something not too expensive, point and shoot, decent pic quality half decent zoom

Failing that any totally waterproof iphone 4 cases?

I use an Aquapac with a few sillica gels in and normal camera.

I have left it in bouyancy aid pocket down this:

It does leak *slightly* on very wet days – hence the sillica gel.

I have uber cheap camera (£22 Nikon S220 from Jessops clearance), and a more expensive Ricoh. On really iffy days / likely swims etc I pop it in my ‘grab’ drybag as well on deck or under seat (In a spec boat or open canoe).
The Ricoh gets way better shots than any waterproof P&S I have seen.
With case on (I can tell cos a couple have the case in the shot!):



Whipped out of case on bank or on easy water:

I just bought a kodak playsport x5 from Amazon £75 plus a 32gb card and remote £100 all in. ill be taking it skiing next week. Seems to have good reviews, up there with gopro etc for picture quality.

Can’t really recommend it, as I haven’t used it in anger yet, but I bought a Fuji XR20 from Jessops for £79 at the weekend…

http://www.jessops.com/online.store/products/80300/show.html

Image quality is OK, not great. Not tried dunking it yet though.