ellipticals are crap. Here is how to cheat on them. Set the resistance to at least 3, then just shift your body weight from left to right, using the elliptical's fixed circular motion to put your other foot into the top position ready for you to shift your weight to push it down. I once did the elliptical for 3 hours and was fine.
Also if you set the resistance too high, it'll mess up your knees after a while.
The best machine for cardio is either an air rowing machine or recumbent bike. which one you get depends on what other exercises you do. I like the rower, but had to get rid of it because I also have a pull up frame I use often.
Honestly, all you need a a set of adjustable weight dumb bells, gloves, a timer, a yoga mat, and a computer or tv that can stream this:
http://www.youtube.com/user/charliejames1975 Shes hot too so it'll take your mind off how much the exercise sucks.