Hi John.
I have a couple of technical t-shirts from Millets - one is a Craghopper, the other is Peter Storm, which I think is their own brand. Both are pretty good, but, as they are more of an outdoors/trekking style shop, they do tend to be slightly thicker material, for walking rather than running, so can be a bit heavy for running in hot weather like we're having now. I like them for cooler days though, and they are better than cotton regardless of the temperature.
http://www.runnersneed.co.uk/shop/enter.html have some Sub4 coolmax shirts for a tenner at the moment. I have some of the Sub4 shorts and love them, and I'm pretty tempted to buy a t-shirt to match.