From Muppet Wikki:

Sesamestreet.org is an official Sesame Street website, featuring video clips, games, playlists, and more. Although the site was scheduled for debut on August 11, 2008, it was on the web as early as August 5, 2008. Clips can be found by grouping by character, theme, educational topic, classic clips, or songs.

This is great! This new site has just about every muppet sketch I can remember from childhood. Most of the muppets are listed, but for whatever reason, they chose not to list Lefty (a.k.a. The Salesman) in the character search list, but he's pretty easy to find. Sure, you can find most of these on YouTube, but the quality is hit-and-miss.

"The Air Salesman" (click image) featuring Ernie and Lefty was always one of my favorites. Ernie finally gets the better of Lefty in "The Ice Cream Salesman," though.

Also, Johnny Cash sings "Nasty Dan" for Oscar and "Five Feet High And Rising" for Biff. Classic stuff!

Sesame Street Videos