Lightweight Wiregates I've used:
Neutrinos (36g) - The original lightweight wiregate biner. A little small. Some people say they are difficult to handle with big hands or gloves. I don't recall having any significant problems with them.
Trango Superflys (30g) - Nearly full size biner. No shroud on the nose of the biner, so rubbing against rock can easily open the gate (TM at Feathered Friends pointed that out to me). Relatively narrow rope-bearing surface (9mm vs. 9.4mm for the Neutrino). Overall my favorite lightweight wiregate biner.
Omega Pacific JC (41g) - Huge rope radius, easy to clip. I haven't used these a whole lot yet, but I really like them. For alpine usage, I'd go with the Superfly for weight reasons. 11g/biner is a lot.
Omega Pacific Dovals (37g) - unique shape is adaptable, but I don't like these biners much. Too hard to tell top from bottom. Not particularly easy to clip.
Wild Country Helium clean wire (33g) - I got one of these for free from some magazine promotion. Haven't used it much, but it seems nice. Clean, no-snag nose. Expensive! $11.50 each!
Black Diamond Hotwire (45g) - full size. Not a lightweight biner. Good standard workhorse biner though.
Biners I haven't used:
DMM Prowire (36g) - shrouded nose. Large gate opening.
Black Diamond Livewire (46g) - Looks like a good clippin' biner for cragging. Not a lightweight biner.
Camp Nano (28g) - Supposedly smaller and fumblier than the Neutrino. Definitely the lightest wiregate on the market.