If you're looking for a retention holster that doesn't look like one, consider the new Blackhawk GripBreak Holster. The three-slot pancake-style holster has a molded Kydex interior and features an automatic locking system. This disengages when the pistol is addressed in a strong firing grip, with the thumb of the strong hand pressing a release paddle located next to the wearer's body. The GripBreak works for concealment, but is particularly well suited to open carry, and comes in both nylon and leather variants.
The open-bottom design allows GripBreaks to fit a variety of Glock and Smith & Wesson M&P pistols. This particular holster is designed for the Smith & Wesson M&P series, and saw serious duty earlier this month at a Blackhawk-sponsored event where Todd Jarrett ran a group of writers through a series of pistol drills. Even with the retention feature, the Gripbreak holster provided immediate release during timed shooting events.
One potential drawback of this style of holster is that it tends to stick out more than a belt-slide style (obviously more than an IWB holster, of course). Getting in and out of your automobile, or sitting at a desk requires an extra second or two of attention lest you bash the muzzle of your firearm against the seat or get hung up on a seat belt. It's not a deal-breaker, but just something to think about with this style of holster.
MSRP: $43.95 (nylon); $78.95 (leather). Both styles are available for left- and right-handed shooters.