Off the top of my head...but Bert doens't seem to have any aquaintiences without Ernie.
- Singing "Take a Rest" with Cookie and Grover (a smash hit by 'The Oz-born Brothers')
- Unscripted bit with John-John
- A honker on his birthday
- Trading his paperclip collection to Mr. Hooper for a soapdish for Ernie
- Asking Simon Soundman how he's able to make tuba sounds out his mouth
- Singing a song about marching with various AMs
- A song about making new friends (can't quite remember the exact title) with Rick Moranis on a plane
Those are the only ones I can think of.