Apparently, Guitar Hero World Tour is the place to be for Nirvana fans as Activision has released the second Nirvana Track Pack for the PlayStation 3, Xbox 360 and Wii version of the game. The track pack includes:

"Very Ape" from In Utero
"Sappy" from the No Alternative compilation
"Stay Away" from Nevermind

The complete pack can be purchased for 400 Microsoft Points or $5.49 via the PlayStation Store. Of course, each of the three songs can be downloaded individually for 160 Microsoft Points, $1.99 on PlayStation Store or 200 Wii Points.