My kids never got to the point of crawling out of their crib. However, I did switch both of them to Big Boy/Big Girl beds(with a side rail) at about their 2nd birthdays. For about a month or so...my son loved it and never crawled out. But then we went through a phase where he would get up and want to come out with us. I just started shutting his door at bedtime(definetly make sure things are "safe" in his room). He would lay by the door and end up falling asleep EVERY night for awhile. Then I would have to go in and move him. I remember calling my mom and telling her how bad I felt that he was falling asleep on the hard floor...and to this day I remember her response...."If he doesn't like it, he will quit doing it". And that he did. It was a short phase and has been fine ever since.
I also think the posters advice about a good bedtime routine with things like bath, jammies, read a few books quietly in bed may help.
Once again it all depends on the child...they are all so different. Just like the whole "let them cry themselves to sleep" thing. Never worked with my daughter, who by the way, had NO problems switching to a big girl bed. YA NEVER KNOW!!! :) Hope maybe some of this works for you. Good luck!
Oh yeah, before I started just shutting his door, I tried all kinds of different ways of putting him back in his bed: sweetly, being firm, rewards...none of it worked for him. I just had to shut the door and let him figure it out!