Here is my collection of Real audio.
I'm not going to put all of the files here, just a few samples.

 
From the album Dookie

Having a blast  (2:43)

Basket case  (3:01)

When I come around  (2:58) 

From Insomniac

Stuck with me  (2:14)

Geek stink breath (2:15)

Jaded (1:30)

Westbound sign (2:12)

Walking contradiction (2:31)

From Nimrod 

Nice guys finish last (2:49)

Worry rock (2:26)

King for a day (3:13)

You'll need a Real audio player to listen these files.
Download the Real player 5.0 here.