I love my Alessi Talon IWB for my Glock 19. It is comfortable and protects the slide from all my stinky sweat in the summer. I also got it used for $20 which doesn't hurt.
Well, I don't own any Glocks but I do own a lot of holsters from different companies IE: SafariLand, Uncle Mike's, Bianchi, Don Hume, Houston, and even Cabela's for a number of other handguns. All in all though, my number one favorite place to go for them is at Bob Mernickle's. http://www.mernickleholsters.com/
Try and PM threegun. He's posted numberous times that he's a Glock fan. If he doesn't pop up in a couple of days, I'd do that. Seems very knowledgeable on the various models and I think he packs heat.