We are going through this with our 20 month old. He is getting up at 6:00 (now I'm grateful it's 6:00 and not 5:15!!) I'm going to try to put something over his window to make it darker in his room....it's so light out now at 6:00 am. I've tried the books and toys....he doesn't care about them. He wants me right when he wakes up. My son doesn't sleep in a crib....hasn't since he was 10 months old...that's another issue :-) He sleeps in a big boy bed, so he gets up and just bangs on his bedroom door until I come and get him. So 'ignoring him' isn't easy when my husband needs to sleep in as late as possible since he goes to work.
I have heard of people using a chart....like the Super Nanny uses on her show. Make a weekly chart, and put a sticker on each day he stays in his bed until say 6:30. If he gets 3 stickers in a row, let him pick a prize out of a box. The prizes could be 'special time with mommy' coupon doing anything he chooses, a Dollar Store toy, ice cream cone, etc. My son wouldn't grasp the concept of this just yet, but I plan on using this technique in the future.
Hope you get some good responses!