Taking an exercise class at my local gym when I'm bored with my routine; the camaraderie and energy helps :-)
Also, I do intervals on a treadmill (or any other cardio machine) to keep things interesting.
If you do weights, you could try changing the moves or the weights and reps.
"There's a difference between interest and commitment. When you're interested in doing something, you do it only when it's convenient. When you're committed to something, you accept no excuses; only results."
"If the world seems cold to you, kindle fire to warm it." - Lucy Larcom, hymnist
"You can't do anything about the length of your life, but you can do something about its width and depth." - Shira Tehrani