Ex Officio makes a very effective line of insect-repelling clothing, which I personally vouch for. In particular, the shirts have long sleeves and are lightweight enough to be comfortable in the hot weather mozzies love. If you check sports outlet places like Sierra Trading Post you can get them for less than list price (which is HIGH); Ex Officio itself also sometimes has sales of last-season's colors and so on through their website.

If you live in a place where mosquitos are common, you might want to try one out.

They even have socks, but I have not been so desperate as that yet.