I struggle with the same thing. My main problem is that the rest of life so often gets in the way. Kids and their activities, my obsession with actually sitting down together as a family for dinner on at least a 5 day/week basis, simple exhaustion from work/family and all the excuses that get in the way.
I finally faced facts and decided that since I am 1) a morning person and 2) not able to carve the time out otherwise, I am getting up an hour earlier in the morning (yes, 4:45 a.m.) to work out on the treadmill and bowflex for an hour.
I'm on day 2. We'll see how it progresses. My goal is 5 days a week, an hour per day. If I get bored with it, there's always the Wii Fit and my bicycle.
Good luck to you finding what works for you in the exercise area. It's definitely part of the fitness equation!