I carry a Kahr CW-9 IWB pretty much year round and it's very comfortable. I often wear those thin polo style shirts, or a short sleeve button down, or even just a tshirt and I don't mean that my usual size is a medium or large, depending on the cut, and I wear a XXL to conceal my gun. My wife has said on numerous occasions, "wow, you really can't tell you have a gun", and she knows where I wear it!!!
It conceals great, I'm accurate with it, reliable, comfortable, and didn't break the bank either.
I would definitely check these out and try to shoot one before you buy something. I will however say that I am a big fan of the Walther PPS as well, but the are at least $200 more than the CW-9.
Hope this helps,
Shawn
Oh yeah, the Don Hume 715 is also a nice inexpensive IWB holster for it too.