That's why the good beers come in dark green bottles! Keeps these pesky UV rays from ruining a good brew. Other than the direct sunlight thing, I have seen coolers with double wall, vacuum insulated transparent lids. They work well enough, as cold air tends to sink and you don't lose too much out the top - but you gotta keep them in the shade. Not good for boats and beaches. Of course you can always cover with a towel or get a fat person to sit on the cover to block the sun, but that defeats the whole purpose of transparency anyway. Plus, when chubby passes out or falls asleep, then you're really screwed.
