I'm just beginning to explore the tedious world of long-sleeved bike clothes, after having several actinic keratoses (sun-related lesions) removed from my forearms. I hate all of them, but the best I've found so far are some CoolMax long-sleeved T-shirts I bought cheap from Sierra Trading Post (sierratradingpost.com; they have a retail store here). They're light and fairly cool and wick well. don't know about their SPF value.
Just about every outdoor clothing company (Sahalie, REI, Cabela's, Scheel's and many others) makes sun-protective garments these days, and I assume most of the big bike-accessory places do, too (I don't wear bike-specific clothing, except for shorts and shoes, so I don't check the catalogs or Web sites). And Grant Petersen at Rivendell swears by ordinary cotton seersucker shirts. The waffle weave is cool and the loose fit lets air circulate. He used to sell them; maybe still does: www.rivbike.com
FWIW, I wear cotton long-sleeved T's a lot of the time. According to cycling legend, they get damp and don't dry out, but generally in the summer, damp is good.