this is the band i have and its awesome. IntoCombat.com carries about 5 other varieties as well. you can get them in various resistance levels, from what would be considered beginner level all the way up to elite or professional.
http://www.intocombat.com/store/prod...p?ProductID=23
i have the orange(elite) bands. if i use only one band its great for warming up. when i put all three on its a tough workout.