hmm, sounds like some rehab would be good. Have you seen a physio? I literally tore my ACL in my right knee in half and after a year of working on it pretty hard, i no longer need my brace and am now back into doing squats, etc. It's still pretty shaky at the heavier weights, but it's not too hard to muscle threw it. I know this doesn't really answer your question, but I can't think of any real effective exercises that would help.
There are always the exercises where your lying on a mat and doing leg lifts, but they are not very good for fast results, like doing weighted exercises.