What is a standard 1/2" compression angle stop? I am installing a sink faucet supply line

Usually they are chromed brass. They are a valve that goes between where the pipe comes out of the wall and a faucet. They have 1/2'' female pipe threads that go to the back and 3/8'' compression thread that goes on the top. If it is out where it shows, it is one of the few places I would use a globe valve. If it is going to be hidden in a vanity or cabinet, I would use a half inch ball valve matching the type of pipe you have, adding an elbow if you have too. Faucets usually have 1/2'' pipe thread too. You may be able to find an angle ball valve.

This is what you're looking for. Regards, Toim

I just bought a couple of BrassCraft 1/4 turn angle ball stop valves for my laundry sink replacement. The look like they will work well. I will let you know after I install them. I got them at Home Depot, in the same section as the normal stop valves.

Here's a picture of one:
http://www.brasscraft.com/Images/0565%20G2%20valve.jpg

From http://www.brasscraft.com/Default.aspx?Page=WhatsNew.aspx :
1/4-turn stops - BrassCraft offers an outstanding value by combining patented 1/4-turn technology, durable construction and proven performance at an affordable price. Backed by service that only the industry leader can provide, these BrassCraft stops are the new twist in quarter-turn. BrassCraft"s new 1/4-turn stop is available in straight and angle styles with a variety of inlet options: compression, iron pipe, CPVC and barbed inlet for PEX.