How to rehabilitate knees from past injury?

[RT]

I injured both of my knees about two years ago in fairly rapid succession (torn meniscus). I am walking fine and can mostly do what I was capable of before the injuries, but am looking to further build up muscle strength in my legs to prevent future injuries and to at least get back to where I was previously.

I don't imagine any sort of high-impact or especially strenuous exercise would be wise (at least initially). I have been biking, and am wondering if anyone could offer further suggestions for ways to rebuild strength in my knees.