At 3 months old, Mia is already trying to roll over. I wish I had a picture, but everytime I grab a camera she stops what she's doing and just stares at the camera. When she's laying on her back playing on the floor, in her swing, or even in her bouncy chair she twists her upper body. She can kick her leg over enough to get herself on her side, but not quite all the way over. According to this video I found on Babycenter.com babies usually flip from their belly to their back first because it doesn't take as much muscle, but Mia hates being on her belly so much she refuses to do anything, but lay there and cry. She does lift her head up a little, but I think that's just so her cries aren't so muffled.
This video gives you a timeline of development for your baby. It's pretty cool.