I recently picked up a t-shirt from wally world,one of the wicking -workout type.It is very light weight,much more breathable than the old stand by I had been using, from REI btw.I have been using it for the last two weeks at the gym (and on the trails around home).After a work out,I find that I'm not nearly as sweaty as with other shirts.The shirt is also tag-less.
Patrick