My DS, who's almost 2 years old, looooooves his cot mobile. We bought a battery operated one (Tiny Love Symphony in motion) and it plays three pieces of classical music. Once he was able to pull himself up in the cot, we removed the actual mobile itself and left the music box attached to the side of his cot. He now puts himself to sleep or self-settles when he wakes up in the middle of the night or in the morning by turning the music on himself. It has been one of the best baby investments we made. If you do decide to get one, I'd definitely recommend getting a battery operated one. The one we have goes for 15 minutes. Long enough to put baby to sleep. Those wind-up ones only go for a minute or so, and you can't use it after they learn to pull themselves up as they can reach and pull the mobile down.
Twins' Mum, VIC, E & A born 4/04