If you're traveling somewhere that's hot enough to melt the funk right off your normal base layer of nastiness, and you need your shirts to do double-duty for urban adventures, check out Howler Brothers. They make respectable threads that really perform in hot weather.
The Magic Mesh polo shirt has been the first shirt in our pack for a couple years now. It's a great topper when you need to keep your cool. The basic polo format, no pockets, has a straight cut that strikes the perfect balance: not too loose, not too tight on a normal athletic frame. The 100% polyester mesh is tight enough people won't notice it in so-called "polite company" but it definitely works to keep you from getting hot and bothered.
The blue design with red stripe is a bold statement, and the monkey logo, which evokes Curious George Gets a Hangover, is a great alternative to tennis club crocodiles. The clincher was on day three of wearing the same shirt, when the Magic Mesh showed me the money: no smell-o-vision, which for a synthetic is where it's at. Highly recommended travel wear.