A no-brainer on this is a musical table by Leap Frog. This has been a big ht with every kid I know that has seen it. We bought it around 5-6 months, and our son used it as a tool to pull himself up and develop standing skills. The musical options originally kept him busy for hours on end. He learned whhat all the different things did, and definitely learned to use the things tha generated the sounds he liked the best. To this day at almost a year old, he still enjoys it quite a bit.
We also have a musical caterpillar by Leap Frog that has notes, classical music, colors and numbers options onit. I think he likes the noises, but I am not hsure that he is leaarning anything from it.