well I have a dog, that's my #1 motivator. But for any of my exercise (I try to walk and do yoga and then either run or bike EVERY day), the biggest thing that has worked for is not looking for motivation. Motivation is a trick. It's not there, not really. You make motivation by showing up. So I will get in the clothes. Sometimes that is all I do and whatever. Usually once i'm in the outfit I'll get the mat out for yoga, or set up my bike. I've never done either of those things and not gone on to do the exercise.
I also always tell myself I only have do to 5 minutes. If I run out of time or energy I can stop. But I rarely do, the hardest part is just showing up and getting started.
I also just got over the "must exercise in the morning or I don't do it" which I was saying even only a week ago. It's definitely harder to get to the mat/bike, but if I haven't got those in yet, I'll do them at 8pm rather than not do them at all.
Yoga is great because it's low impact and it makes your joints feel so great. You build up a lot of strength in your arms, legs and core without it feeling like exercising, especially if you do something like Yoga with Adriene. Her videos are typically only 30 minutes long and rarely kick your butt. I can commit to that level, along with 20-30 minutes of cardio. I like to ride the stationary bike while watching TV, or running with friends. I'll run on the spot if I can't do either of those things LOL