Any recommendations?  Quick googling seems to show that Chums and Croakies are leading contenders...  Anyone with experience with either of those?  Others?

I heartily endorse both brands, but with two caveats.  I don't normally wear a sunglass retaining strap while fishing, but I do while whitewater rafting--I haven't lost my Oakley's yet--and I also don't use the floating style.  I normally use just the simple strap, like pictured below.

Mine is long enough that you also use it to hang your glasses around your neck comfortably, while not wearing them.

 

Bass Pro Shop and Cabelas sell "special" Chums/Croakies, and maybe their own brand, for fishing.  The ones that I saw were made out of thick monofilament fishing line, and looked like they would work just like the ones I already had.  The one pictured below is the Chums Mono Orbiter.  It's shown in black, but it comes in six or seven different colors.

 

I was able to find them using a quick Google search from several different online retailers.

I got a pair of Chums from Don at the canoe outfit in Front Royal.  They're definitely capable of floating the heaviest spectacles you care to put on your nose.  My sister gave me one she got at Dollar Tree, and they work fine for plastic lens Oakleys, and more comfortable.  They held up all last year too.