Well, funny you should ask ... I have gravitated towards polo shirts in the last couple of years for warm riding, and I bought a few from Lands End last year, and that's what I brought to LA with me.
I also have a couple of LS seersucker shirts with me here (wearing one as I type), which I love for warm weather riding, for the UV protection and keeping the material from sticking to the skin. I've not tried chambray. Madras doesn't work for me, tends to really cling to my skin. Haven't tried poplin, probably worth giving it a go, and probably looks a little neater than always-wrinkled-seersucker. I like the knit polo shirts, so far, they seem to really breathe well.
I've noted elsewhere, I think, how happy I am with my wool polos from Minus33 and Smartwool (a blend, actually).
The photos of me from the LA ride yesterday show me in the long sleeve white Lands End polo, which I especially appreciate on a sunny day for its UV protection. Basic cotton, might have come from their school uniform catalog.
Also got this short sleeve mesh on sale, and it appears to still be there, on sale. Not fully happy with the way the sleeves fit, middle of biceps so they tend to climb up.
And I got this basic light blue (hard to color balance this), again not fully happy with the sleeves on it. But I like the performance of the fabric, and I like how normal they look on and off the bike. All of them have long enough tails that I don't feel too drafty in back.
Ted Durant
San Marino, CA USA (for now)