What to get a 4yr old boy for his brithday?

My younger brother turns 4 in July, what should I get him? He's the type that some toys he will play with once and never touch again, or he goes gaga for it and won't put it down. Some of his favorites include a Styrofoam sword, binoculars, a hotwheels bath toy, small plastic ponies, and any sort of bouncy ball (particularly the large colorful ones). He also enjoys movies such as Cars, all Scooby Doo DVDs, Spirit, Shark Tales, and Rango. I want to get him something he will enjoy for his birthday, but really have no ideas yet.