I like the DeSoto Cool Wings with tank tops when it's really hot outside. I've also tried Craft sun sleeves with a lightweight short-sleeve jersey on days when it's kinda hot but not too bad (temps in the 80s). I bought the Craft sleeves because a friend has tried several brands and likes them best.

I've considered buying the summer long-sleeve Canari jerseys but haven't tried them yet. It does seem that several companies are making nice light jerseys these days, much more comfortable in hot weather than most jerseys used to be. I hope you find some that you like.