Looks like there were several releases on Rock Band over the last few days. First up is the PAX Collection 01 for 240 MS points, or individually for 80 MS points each. This pack includes "Skullcrusher Mountain" by Jonathan Coulton, "Shhh...." by The Darkest of the Hillside Thickets, and "Livin' at the Corner of Dude and Catastrophe" by MC Frontalot.
The other DLC that came out last week was Locksley Pack 01 for 240 MS points, or individually for 80 MS points each. This pack includes "All Over Again," "Don't Make Me Wait," and "She Does" by Locksley.
If you like to experiment with new music on the cheap, then these packs may be something to look into.