He role-plays that he is Caillou, Sam is Rosy (Sam has no clue!) and one of our cats is Gilbert. Sometimes Mommy and Daddy get to play the roles of Mommy and Daddy too.
With my old Barbie and Ken dolls, he plays house. One particular Ken is Daddy doll and usually Ekaterina (doll based on figure skater Ekaterina Gordeeva) is Mommy doll. Sometimes his Little People get to be the kids. We're flattered that I'm Katya and Chris is Ken.
He loves giraffes. He has lots of giraffes and has made a family with Mommy, Daddy and several baby giraffes.
He re-enacts scenes or makes up his own with his Cars and Nemo and other characters. He even substitutes other cars or critters to fill in the gaps for characters he doesn't have. Currently, he is also obsessed with Elmo, Mickey Mouse and Winnie the Pooh. He has Mickey (Sam's, but Sam let's him play with it) and Goofy; Elmo, Zoey (Mommy's), Cookie Monster (Sam's), Grover (Mommy's); Pooh and Tigger. The others he makes up with Raffe (a giraffe, what else) and other stuffed animals role-playing.
I love that he not only pretends and makes up stories, but he is able to imagine a toy is something or someone else.
Of course, the 'dark' side is that he sometimes passes blame. I don't think he understands what he's doing, because he seems to think it's all just part of pretend, but he will blame Daddy, while Daddy is at work, for something happening. When I remind him that Daddy isn't home, he corrects himself and tells me Wil did whatever.