Got the wife an early birthday present (her b-day is next month). The old treadmill was about worn out and she wanted to go a different route, something less strenuous on the knees, low impact. Well I just got my exercise putting together her new NordicTrack E6.3 Elliptical.
I tried it in the store and it doesn't really hurt my knees so I may have found something I can use to work on my lower body.
You will feel it in your thigh muscles though - they are great.