Petzl - Color coded carabiner gates
A nice detail on Petzl carabiners:
The double action twist carabiners have RED gates.
The triple action twist carabiners have ORANGE gates.
You can look at your harness at a glance and know what you're grabbing. Is it mandatory? No. Is it a nice design touch? Yes.
Petzl Sm’D twist lock, my favorite for a personal tether. Once it clicks shut, you KNOW it's locked. Bonus: If you look closely, you can see a tiny hole drilled underneath the gate. If you’re a keeper-cord kind of person, this gives you a convenient place to tie one.
Petzl Rollclip, a combination triple action carabiner and (fairly) high efficiency pulley. Useful in various kinds of minimalist rigging and mechanical advantage systems, very cool tool.
(Side note: Please don't top rope through a pulley carabiner like this. The decreased friction increases force on the anchor, and makes it more difficult for you to control the lower of your partner, among other things.)