http://www.mameworld.net/maws/srch.php?control=7
All MAME lightgun games.
Actually, I think that list is all MAME gun games -
First off, there are two types of games -
Positional Games - These basically had a machine gun mounted like an analog joystick. I'm pretty sure T2, and some of the Operation (Wolf, Bear, Thunderbolt?), and maybe Revolution X used this type of control. These can be played (less realistically) using an analog joystick. They might be able to be played with a lightgun, but that is basically a hack to play the game with improper controls.
The other category is true lightgun games such as Area 51, etc. These could be played with a mouse, but really want a true lightgun.
For the guns - I think all of the guns also run through the video cable as well as plugging into the USB ports. KevSteele has a review of most of the options at
http://www.retroblast.com/reviews/lightgun1.html There is also a lot of WIP going on to add support for the Namco PS2 Guncom 2 to MAME.