It might seem a funny question (we discussed something similar on PPRUNE once before) but are there any aircraft that float? One might imagine that some of the foam/composite types should be reasonably buoyant though I'm guessing the CoG would tend to tip them forward.
There have been a few instances of composite gliders being ditched in fresh water (I don't know of any that have actually been ditched at sea!) and the consensus is that, while they tend to submerge briefly on impact, they float for several hours while water slowly creeps into the empty spaces making them less and less buoyant. They have no CG issues as without an engine up front they are inherently quite well balanced. The wings also provide lots of lateral stability, much like a canoe with very large floats on both sides.
They're usually able to be dragged near to the shore before they submerge completely, making recovery easier. That won't make repairs that much cheaper, though.
Cheers,
DG800