Splash and big thunder are perfect. They're like the pre-cursor rides to ca screaming and ToT. When I was a little kid I LOVED splash and big thunder. I felt like a big kid cause I could handle the "drops" and "speed" of the coaster. I think your 3 yr old would like those two rides. Pirates is also a must, I went the other day with a group of friends and these two little kids sat behind us with their parents and after the first drop they were giggling wildly and yelled "CAN WE GO ON IT AGAIN!" they were probably around 3 or 4 and it made the whole boat smile.
My 3 year old (now 5) loved Soarin'! It's just an easy glide, and the smells make it so fun! Don't forget about the Rider Swap program. We took advantage of it on our last trip, and it made it so that we could ride a few of the 'bigger' rides without waiting in line twice.