For those of you who were offering advice on 'big boy beds' - we went with a toddler bed. For a couple of reasons:
Cost: inexpensive to buy (Costco) and gets us another year or so of use out of his crib mattress (which is a good one) as well as the wool duvet and flannel crib bedding I splurged on.
Size: As his current room is small, I felt that taking up as little space as possible was a good choice now, since our house doesn't have a rec room or finished basement his bedroom is also his play room. We are considering moving him to a larger room in a year or so and then we will look at a larger bed.
I also liked the idea of the side rails and his ability to climb in and out of it on his own.