One thing i'd like to point out is for very hot weather - try a good summer/heat baselayer by Craft, Giordana, Pearl. I know it sounds counter intuitive but they exist for a reason. They're made specifically to cool your body down.

Twice a week I ride out of where I work in North Jersey because of the mountains. These kinds of rides are ones where you're going 9 mph or 38 mph and very little in between. This season I started wearing a wicking baselayer during hot days and it really does work. Yes you obviously sweat but you never feel overly hot and I think that is the key to their existence. Geez, now I feel nake if I ever get on the bike without one!

I have the sleeveless Giordana for the hottest weather and I love it: http://www.competitivecyclist.com/za...130&MODE=&TFC=

And for weather up to 75*F, I love the Craft short sleeve. I like this because the sleeves are slightly longer than jersey short sleeves so you can tuck them up or they anchor arm warmers very well if it's cooler outside: http://www.performancebike.com/shop/...tegory_ID=1123