I daily carry a Glock 26 IWB with my shirt tucked in using an MTAC holster. It does not matter if it is a t-shirt, golf shirt or dress shirt, they all tuck in and become virtually invisible. In the 8 months I have been using it, I have never been called out, and I cannot rave enough about how much I like this holster. It holds the gun firm, and allows you to adjust how much it grips. I always have a round chambered and never worry about the lack of a Glock safety. Here is a link to the one I have. They have some slightly less expensive models that I hear great things about as well.
http://www.comp-tac.com/product_info.php?products_id=95
I really recommend the MTAC from Comp-Tac. It is very comparable to the CrossBread, which is also a great holster. There are two reasons I prefer the Comp-Tac. First, it is
made in Texas whereas the CrossBread is made in Missouri. I prefer to keep my money in Texas when possible.
Second, they do have local dealers. You can look at the link above to find one local to you. I don't see where you are from, but if you are in Houston you should head over to Collectors Firearms and ask for Alex. He is their Holster expert. He will spend some time with you and make sure you get the right holster.