Metropolis is cool but it isn´t that hard. If you really want challange try to learn Dream Theater´s Dance Of Eternety. I never tried it ´cause you´ll have to own a 7-string axe.
Malmsteen´s Rising Force (his first album) songs are amazing as well as Vai´s songs like For The Love Of Good, Audience Song, Erotic Nihgtmares, Satrianis Surfing With Alien, Summer Song, Always With Me...
Almost evry instrumental tune by guitar master players are amazing guitar songs. But unvirtouso bands can somtimes be really cool like the last one I learned a couple days ago was Queen´s old classic Bonhemian Rhapsody. I arranged the piano parts to guitar and some of it sound really cool not to mention the ending riff wich kicks ass. Solo is very very easy, actually whole song is damn easy but it´s cool especially if you can sing along.
Dejan S. No speed limit