We can all find ways to be busy, but when it comes to exercise, here is what I have found helpful. Take note that I am a stay-at-home-mom of two children (but I found ways to exercise even when I was working full-time).
1. Don't let your children be an excuse. When my first child was a baby, I would exercise when he napped. I then invested in a nice jogging stroller so he could run with e.when he was a few months old. Now I have two children and I push a double jogging stroller as I run. Yes, it's a lot of work and I can't run as far. BUT, I'm still getting a workout in. I live in the Midwest, so running outside with my children in the winter is not an option. I workout in the basement on the treadmill and/or doing weights while they play (when they were younger, I would sometimes workout to a video if I felt it wasn't safe to be on the treadmill around them).
2. Invest in a good jogging stroller. Yes, they can be expensive, but if you have kids, a good jogging stroller is a must (and the only stroller you really need). The best one out there (in my opinion) is the BOB revolution. You can lock the front wheel straight or allow it to move around. Even the double stroller (side by side) can easily fit through a standard doorway so you can take it shopping too! The back wheels easily pop off so you can fit it into the back of your car.
3. Invest in a good treadmill. Face it. There will be weather days that will keep you from working out outdoors. Don't let that be an excuse. Get a treadmill, and, honestly, not just any treadmill, but a good one. It doesn't have to be the most expensive, but a good treadmill will make a HUGE difference in how you experience your run. You still might not love to run on the treadmill, but you won't hate it as much either. ;) Things to look for: a long tread belt (you don't want to be worried that you will fall off the back), a built-in fan (cools you off and makes you feel like you are running outside), speakers with a place to plug in your iPod/phone/etc. (now you won't have to worry about headphones or where to put your iPod/phone/etc. while running!).
4. Invest in some weights. It is SO important to do strength training along with aerobic training. Stop by a sports store (even a Target) and get some weights. You only need a couple different size weights and you can workout your entire body.
5. If all else fails, join a gym and find some classes that motivate you. If you have kids, make sure there is childcare for them so they don't become your excuse. I also highly recommend hiring a personal trainer for a few sessions to give you some ideas on how you should workout in order to meet your fitness goals.
Even if you don't have kids and/or work full-time YOU CAN DO IT! I used to wake up at 5:00am every morning to workout and take a quick shower before heading off to work, because I knew I would be too exhausted (and less motivated to do it) after work. Take a good look at your schedule, make some changes, and get going. NO EXCUSES!