I don't have any Sesame Street toys that have been produced in the past ten years, but I guess you can't go wrong with Tickle Me Elmo or any variations (is the original Tickle Me Elmo still being produced?). Or those anniversary plush that came out a few years ago. I'd also recommend the Sesame Street Beans that came out in 1998, the Magic Talking Kermit, the finger puppets from the 1970s and 1980s, and the die-cast Sesame Street vehicles which I think were released by Playschool in the 1980s. Of course you'll probably have to try eBay or search flea markets and goodwill stores for those.
I think it'd be easier to pck out books and DVDs. You can't go wrogn with The Monster at the End of the Book, and there is a book called the Sesame Street Treasury, which combines many books from the show's 40 year history (including How to Be a Grouch and The People in Your Neighborhood). When it comes to DVD, I'd suggest Learnign About Letters, Learning About Numbers, Monster Hits, Big Bird's Storytime, Silly Storytime, C is for Cookie Monster, Bert and Ernie's Word Play, A Celebration of Me Grover, and any of the anniversary DVDs.