FN P90
The new weapon, in case you didn't follow the link in a previous posting (which may have been good, or not -- I didn't look), is a Heckler and Koch FN-P90 submachine gun, which is an experimental weapon capable of piercing up to 42 layers of Kevlar with the right ammunition. O'Neill mentions the "new P-90s" about four episodes in advance of Prodigy when they have to go out to some apparently dangerous planet -- I don't remember the details.
Some specs on the gun itself: the muzzle velocity of the P90 is 750 m/s or, for you Americans, about 2500 f/s. That's fast, very fast. It has a firing rate of about 20 rounds a second if memory serves, but don't quote me on that. The ammunition is stored in a rear-loaded magazine that doubles as a butt, and can take up to 250 rounds, while the weapon weighs a considerable amount less than an Uzi fully loaded. The P90 is equipped with a built-in suppressor and laser sight, and I think is accurate to over 1.5 km. Some of that may not be entirely accurate, but that's the general gist. This weapon is much sweeter than the old HK MP5s, and personally I think it's a lot more photogenic -- at least, from the point of view of a designer, that's a damn nice looking weapon.