Be careful with the elliptcal. Your stride needs to be aligned properly, or it can cause knee pain. I had this problem.

Push a box across room/ side straddles on a bosu. Slow Step ups on a bench w weight / SquAts and lunges (carefully)/ and wall sits. Tons of cardio you can do at the gym without aggravating knees.

Try the ropes, if you have them at your gym. D jacks w dynamax ball. And others have mentioned more standard stuff like cycling/ swimming / rowing and elliptical. I don't run or jump on a box as these agravate my knee arthritis.

My ortho says elliptical and bike are okay. He prefers 15 minutes of each rather than 30 minutes straight. I also do water aerobics and swim. I've had good luck working with a personal trainer who was able to really push me but also keep my knees feeling good. Spendy but worth it in my opinion.

Good luck.

water rower (ie, rower where the wheel is water not air based)

I have bad knees but no arthritis. Swimming and biking are the main 2 exercises ortho surgeons will recommend over and over again because they are low impact.

PP of an indoor rower is a great workout and much less impact than running, but depending on your pain, might not be a good option based on the motion. Worth a try, but cautiously.
Pilates would be an excellent way to get the strength you need while (most likely) reducing pain. Find a great studio and take some reformer classes. It is expensive but so worth it.

I know you want to focus on cardio but strength training is going to make a big difference in keeping your knees healthy and helping drop excess weight.

Check your gym/country club or local recreation center for water aerobics or water exercise for those with arthritis. Saw such a class on the schedule at springhill rec center in McLean if that is convenient. Best wishes for your continued healthy life style and weight loss!

Get a Concept Ii indoor rower. Excellent overall workout with little to no stress. You can do a few minutes at a time multiple times a day to build up endurance. Works a large selection of muscle groups legs thighs butt abs and shoulders

Cathe friedrich has some great low impact dvds

Congratulations on your weight loss. I also have arthritis in the knees and find that plain walking helps, at least a mile a day. If I skip a day I'm sore the next day.

swim laps

I have bad knees, but not arthritis. It has really helped me to do squats and lunges to strength the muscles around my knees. I have to listen to my knees though, and I don't over do it. I would never do these exercises if it weren't for my personal trainer guy standing there and telling me to do them though. I don't really like squats and lunges, and I thought I shouldn't do them because my knees were bad. He said that is exactly why I should do them so that I have muscles around my knees strengthening them.

On you tube there's a woman named Jessica Smith who has some good videos for people with bad knees. Check it out.

Biking?

I had a recent CAT scan that unfortunately showed arthritis in both my knees which explains the problems that I've been having this last year- I have been working hard towards losing weight I am down 15 pounds and have 15 more to go. Now that the nice weather is here I want to start exercising but I need something that is cardio but easy on my knees suggestions please?