Actron Pocketscan. That's what I have. I never checked for compatibility. My buddy had one I tried it and it worked. The codes in the back of the book help. There are also Subaru specific ones: Subaru Trouble Codes - 1996 & newer Subaru-specific OBD-II Trouble Codes
The Pocketscan is the cheapest and will do the trick, the more expensive ones just have more buttons and will actually display words on what the code is vs just the code.
This little guy is worth it too for when you go to get your yearly emmisions tests. It will tell you if you have any problems so you don't waste your time at the inspection place being told you have failed!