Pretty critical gear category that seems to be missing. Shirts have gotten so technical over the past few years and it makes a big difference if you are out on a wall for 10 pitches in so-so weather. I am a big fan of Mountain Hardwear's Transition Featherweight Zip T. First of all zip neck is a must for me so as to quickly adjust temperature modes. Outside of adding or removing your hat, there is nothing that can regulate your temp quicker then letting the air hit your chest and neck or not. Tight fit is also essential for rock climbing. I used a loose Patagonia product for years (Regulator), and although I loved the fit and feel, I contantly snagged the sleeves on sticky rock and tore them to shreads. Should be all kind of competitive products out there to discuss. Please only add shirts with technical features and leave casual attire for another web site. Thanks!