Having been afflicted with the Curse of the Gingers at birth I too am often searching for long sleeve protection from the sun, especially for summertime adventures. I can only speak to two things I've tried, and one thing I'm going to try...
1. Under Armour Heat Gear (in white, slim-ish fit): Light. Airy. Super easy to stain with dirt that never washed out after one use. Smelled so bad after a weekend trip with some humidity I thought I would pass out, which is saying something because, as a friend once said, "everyone loves their own brand." It was that bad; trashed.
2. Arcteryx Motus LS (in silver, purchased 60% off at REI): Expensive before discount. Totally made of some sort of unicorn hair spun into a magical garment that works great as a base layer, but more apropos to this discussion, is really amazingly nice in warm conditions. Better yet? Zero stink after 4 straight days of wear 24/7. Unicorn hair I tell ya!
3. Railriders Eco-Mesh Shirt (someone will mention it, but I haven't tried it): Looks promising with it's mesh panels albeit it a little at the expense of wearing mesh and sending the woodland creatures the wrong idea. I may never try it because it has a nehru collar and if I ever caught myself wearing a nehru collar I'd be forced to kick my own @ss for talking about adjusting my chi (what happens after everyone wears a nehru collared anything).