I did knit a summer sweater, tank top style, in angora and bamboo a couple of years back, it's very comfy in Texas during the summer. Also you could try a bamboo/silk or bamboo/cotton mix which breathes very well based on other tanks I've knitted.
Knitting to keep my sanity. It's working... kinda...
OTN: Dr Watson's Cable Crew Neck
OTN: Writer's Cardigan