Any MuppeTelevison epsiodes of The Jim Henson Hour.
The complete Dog City episode (with Jim Henson Hour bumpers).
The promo for the playhouse videos from 1985, which were shown after the programs ended (there were three different promos, but the main difference was that each promo was longer than the previous one, and at least in the preview following Muppet Moments, two clips were replaced in the part shown in all three promos).
More clips from the Play-Along Videos.
The Great Santa Claus Switch.
Obviously, more Sesame Street stuff not available on existing videos or DVDs.
The Muppets: A Celebration of 30 Years (it's been a long time since I last saw that special, and all that's on You Tube is one montage).
The Muppets Celebrate Jim Henson (the finale was included).
Great Performances: The World of Jim Henson (I've never seen the whole special... probably just 90 percent of it)
Inner Tube
Sesame Street's All-Star 25th Birthday: Stars and Street's Forever (I only saw most of the whole special when it first aired... stupid tape stopping in the middle of it... and missed the first few minutes).
Out to Lunch (fat chance of that happening anytime soon).