What's a good BIG gift for a baby that will be 18 months old at christmas??

my son will be 18 months old at christmas... by big gift i mean like the Santa Gift.... my family does christmas where santa always brought us one BIG thing.. then mom and dad had the rest of our presents from them under the tree.... i have NO clue what to get my.... i havent really saw anything that i really liked.. i've already got him Elmo Knows My Name... hes crazy about elmo and the teletubbies and he will occasionly watch barney....hes not a typical 17 month old... hes 3 ft 3 inches tall and 37.5 lbs... he's like the size of a 3 year old.... and he's ahead in talking (for kids his age)... any good ideas... HELP ME!? lol