I actually bought a red cross shirt from the red cross website a few weeks ago and it was printed on an AlternativeApparel t-shirt.
I really liked the feel and weight of the t-shirt, so I looked them up. The AlternativeApparel pricing is a bit high, but I dig the quality of the shirts and the shirt I bought had that "vintage feel" that a lot of sites seem to be going for.
The style of their website is pretty similar to AmericanApparel though, but their clothing line is a bit different.
My neighbor said he used them for a large run of shirts and had some problems with inconsistent color and a few other things, but I haven't tried them out wholesale-wise yet.