I'm on my third baby, and my favorite thing this time around was a sound machine. My mom bought it, it's just a small circle that does different noises. The heartbeat was a life saver when baby was a newborn, and then I switched to the ocean noise around 12 weeks. As soon as I turn it on when I'm changing her diaper for nap, she starts rubbing her eyes! it's terrific!
I love my play gym. Otherwise, nothing much. I didn't use my swing with my second and third kids --they just take up too much space! The play gym can easily be moved, it encourages body movement, etc. The swing is good for a few weeks, why bother! I do also like my exersaucer.
other than that, I couldn't live with my baby carriers.