You've already received a lot of opinions and I'm going to add one more.
http://www.fishpondusa.com/sagebrush.cfm

I live in Kentucky and it gets hot in the summer. I like a vest but the traditional ones are no fun when it's 90 degrees outside. I tried out a couple chest packs and they never made it out of the store. I tried a couple fanny packs and it always seems that whatever I want when I want it is not easy to find or the pack has moved to the side or to the back or shifted or the darn belt is too tight.

I settled on the Fishpond sagebrush mesh vest and haven't looked back.

I would advise you to check one out just to see if would work for you. What works for one person may not work for someone else (thus the multitude of various vests/packs/gadgets out there).

Jeff