In the show that was on last week where that guy followed JD around all day playing that song on his guitar (when they work the night shift and end up in charge of everything)- the song is called Overkill and is also by Lazlo Bane with that guy who is called Colin Hay.
just to clarify (correct) Gaby's response here...
The theme song is by Lazlo Bane, which is a band, not a guy.
Colin Hay followed JD around in an episode, and he wrote "Overkill" back when he fronted the band Men At Work. The song Overkill and colin Hay have nothing to do with Lazlo Bane... other than that they both appear on the Scrubs soundtrack.