I had to go through Physical Therapy many years ago for my knees.
Jump to today and I still remember some of the exercises they had me do, one of them was the straight leg raise. It works your quads (the four muscles on the front/sides of your thigh) and I lost an inch in my thighs just from doing these for a few weeks!
Check it out!
P.S.- I do these in bed before I go to sleep! How convenient!