At 3 my son too enjoyed playingwith the thomas train track set. He still plays with them at 4and1/2. He also loves building with blocks (3-5 yr old lego blocks), keeps him busy for ages.
Do you know if the boy likes books ? My son loves books and i am as fond of the topsy+tim series as he is. Books always make great gifts - you could try to find out his favourite character and get him books. You get books of every character these days - sesame street/barney. I even saw a "CARS" book at the "book buddy" store next to toys R us in ocean terminal.