#2
Just play the same thing? That'll already sound awesome. Meaning, any 1 guitar song will do.
#3
Is this for classical guitars? 2 Electrics? One electric, one bass?

I'm going to go ahead and assume its for 2 electrics, so:

Lay Down - Priestess
Reptilia - The Strokes
Freya - The Sword

While these may not originally be for just the two guitars, they can still sound great without the drums and bass... probably.