Definitely exercise helps. Working out first thing in the morning is probably the best way to ensure you'll be a) energized to start your day, and b) tired enough to go to bed at night. However, that might be tough if you already are on a deadline to get to work.

I wouldn't recommend working out at night if you're already a night owl. If you're at all like me, you'll end up super-awake right when you should be going to bed.