Wayne Brady came back and Ben Vereen guest-starred on the episode "Cleaning House." They are seen here with Barney.
Added:

How I Met Your Mother Season 6 Episode 2 Quotes

Guys, I know you count the minutes until you can escape from your hum drum lives by hearing how awesome mine is.

Barney

So this chick and I are going at it behind the Central Park Zoo, the bonobo chimps are giving us a standing O and just when I'm about to give her the same thing - what up?

Barney