They sang a lot of fun songs including "the greatest TV theme songs" and "the greatest rock and roll songs." Here's a better view:
It's "The Blanks!"
Ted's band, from Scrubs! That's Sam Lloyd on the left, he plays Ted. They've appeared on several episodes and Paul Perry (standing next to Ted) was nominated for an Emmy for writing the song "Guy Love." It was an enjoyable concert, even though it was a cappella. I'm never going to hear the theme song for "Charles In Charge" quite the same way again.
Sometimes that can be really nerdy and annoying.