#1
The only one I've seen is the Jackson Roswell Rhoads.
Do you know any more guitars made of aluminum?
Do they sound ok?
#2
If (the) God(s) wanted guitars to be made out of aluminum he/she/they would have made trees out of aluminum.

DON'T PANIC! DON'T PANIC!
THEY DON'T LIKE IT UP 'EM!
#3
Kramer made guitars with aluminium necks in the 70's, and James Trussart makes electric guitars made of steel.

Also, resonator guitars, like Dobros are mostly brass, I think. Not aluminium, but still FOCKIN' METAL