I wish I could learn the accordion. I was given one a few years ago and it was just too difficult to figure out. And I play piano, so you'd think I'd be able to figure out at least one side of it.
There are some KICK-ASS songs out there with accordion. Barenaked Ladies use it all the time. The best use of accordion in rock is by the now-defunct band
Moxy Fruvous. Check out their album "Live Noise," specifically "Jockey Full Of Bourbon" and "Video Bargainville" for some rockin' accordion.