Knee injuries are frustrating! After I had both menisci trimmed and knees scoped for osteoarthritis I had a little experience with this challenge too.
While you are gym shopping, ask if they have a hand bike. I think it may go by another name but basically, you pedal with your hands.
http://www.amazon.com/%60Hand-Cycle-.../dp/B000LX2K36
These are effective in maintaining our cardiovascular endurance during the recovery period of a lower body injury. I wouldn't use it as my only source of cardio though. Overuse of the shoulders would be a concern of mine...I would crosstrain between the handbike swimming and the recumbent bike if these are options for you as well.
In time, the elliptical is another good option for recovering quad/hamstring strength and endurance without the impact that running creates on our joints.
Vsit a few gyms and request a day or week pass to see if you like the environment and if the equipment is what you need for your successful recovery.
Best of luck!