Lacerta said:
I would have to get up at 6:00 AM to get my exercise in before work, and that would last about 1 day before I would give it up. I

my sleep too much.
I leave for work around 6:50 AM (if I'm not running late) M-F, so to fit my running in, I get up at 5:15. After getting home around 5:30-6:00, I try to get to sleep by 9:30, but that turns into 10:30 most nights.
Fun? No way - I'm not a great morning person, but I've learned to become one. Necessary for me? Absolutely. From the beginning, I've always strived to exercise first thing in the morning, even if it means giving up sleep (and it typically does), because daily exercise is an essential ingredient to my success. By getting it out of the way first thing, I don't have to worry about finding time later in the day, possibly talking myself out of a workout if I've had a bad day, or anything else. That extra 45 minutes I schedule for running in the morning by getting up early is
just for me and no one else, and I've decided that it's worth giving up a bit of sleep to make that commitment to myself.
Also, if I left my main workout of the day for after work, I might be tempted to talk myself out of it some days - no good! It would also be a PITA to have to shower twice a day, once in the morning, and again after my running workout - exercising in the morning solves that problem for me.
Curves workouts I fit in right after work Mon and Wed, and Saturday mornings (again, first thing). Some days it's a tight fit with other activities (and crappy commutes), but it's another commitment I've made to myself, so somehow I make it happen.
However, this is what I've figured out that works with my schedule and keeps me motivated. Find what works best for you, and go for it! The only "universal" advice I can offer is to put exercise into your schedule like an appointment, and then
keep it! It's an appointment with yourself to get healthy - few things could be more important!