On the elliptical I choose a higher level - manually - and then challenge myself to keep the rate at a certain level. I find that I really need upbeat music. Plus I often close my eyes and try to get into a "zone" where I'm not paying attention to the time.
On the treadmill, I sometimes go for the programs, other times just alternate faster times with somewhat slower, or work my way up the incline and back down.
Basically I just try to play with things to keep it less boring and still get a good workout.