M9A1 - Railed frame with a 92FS slide (3 dot sights). The front of the frame (where the rail is at) looks like the Vertec model. But it has the standard 92FS grip. The magwell also has a slight bevel, and the rear and front backstraps have a light checkering on them. Available in 9mm only, and this gun is only made in the USA.
This gun comes with two specially PVD coated 15 round magazines (which are expensive when bought separately).
I think the M9A1 is the coolest LOOKING railed model. But, the checkering is not deep on the frame, like it is on a 1911. I personally prefer the regular serrations, as I find that they give a better grip purchase.
90-Two - Commonly known as the "90-Dash-Two" or "The Dash." This is a redesigned version of the 92FS that came out in 2006. The slide and frame were redesigned. The guiderod is captured, and there is a recoil buffer built into the frame. It also has a front, dovetailed sight. Several of the small parts are totally different from the standard 92 design (hammer, mag release, trigger bar, slide safety switches).
The biggest difference is the grip. While the gun is not polymer, it does come with a polymer, slip on grip. This gun will be in limited production for 2011 (so get one now if you want one). There is hardly any aftermarket support, and the lack of aftermarket grips is really hurting sales. These are ONLY made in Italy. Available in 9mm and 40 cal. The gun comes with factory 17 round mags (in 9mm)
(I personally do not like the polymer grip - too slippery. I tried several solutions to this issue, but found none worthwhile)
92A1 - Newest release of the 92 - Released in the summer of 2010. This design takes some of the best aspects of the 90-Two... The rail, internal recoil buffer and dovetailed front sight (all great changes), and puts it into a more "normal" 92 frame. The 92A1 (and 96A1) will use standard Beretta 92 grips. The trigger guard is curved; however, like that of the 90-Two. The guiderod is also captured (which is a pro or con, depending on who you ask).
In addition - the slide is a little bit beefier than a standard 92 slide.
The gun is available in 9mm and 40 cal (the 96A1), and the 9mm version comes with THREE 17 round factory mags (the same mags that come with the 90-Two). These guns are only made in Italy.
This is a such better choice to the 90-TWO, IMHO. Also, the 92A1 balances the best in a 1 handed grip out of any of the railed models. I also personally find the 92A1 is my second fav Beretta 92 variant - right behind the standard 92FS (which balances the best 1 handed, IMHO).
There is also finally aftermarket night sights for the 92A1 from Trijicon now. And, while others may disagree - I personally like the regular front and rear strap serrations over the checkering on the M9A1. The checkering is rather shallow - so its not nearly as grippy as checkering on a 1911. I think the standard serrations on the front and back strap give a better grip.