In Patch 3.0.2, all bats now have Sonic Blast as their unique, bat-exclusive ability. It's a 2 second stun with negligible damage on a one-minute cooldown. As far as Hunter pet abilities go, Sonic Blast is pretty run-of-the-mill and isn't significantly great to merit taming a bat for. It pales in comparison to the Ravage skill of Ravagers, for example, which is on a 40-second cooldown. Ravage is melee range ability while Sonic Blast has 20 yards -- an irrelevant bonus considering our pets are almost always at melee range. It's only a little better for chasing and stunning, but otherwise, I would much rather have it available every 40 seconds than have some extra range.
Another cool thing in Patch 3.0.2 is that all pets have talents now. Bats get the Cunning talent tree, and you can learn more about the different talent trees in Daniel's Scattered Shots. He considers Cunning pets to have the best selection of talents for PvP -- which sounds just perfect for me. Notable PvP talents include Boar's Speed, Dive, Lionhearted, and of course, Bullheaded. A Bat works well with a Beast Mastery Hunter or at least one with Intimidation, allowing two stuns on separate 1-minute timers (or shorter with Longevity).
There are no unique bat skins, the closest one being the all-white Ressan the Needler and the rare spawn Blind Hunter from Razorfen Kraul. Unfortunately, this skin will soon be commonly found in the bats in Zul'Drak in Northrend, making white bats less unique. There are also red bats, brown bats, and pretend-white bats all over Azeroth. With Bestial Wrath, bats can take up a lot of space with their wingspans and are fun and confusing to take into instances with bats since they usually clump together. Confusing my party or raid is one of the most fun complaints I get as a Hunter with a bat pet. If you're a Hunter with a bat, chances are you like mayhem, anyway. Happy taming!