More than you'd ever want to know about aluminum in a lifetime: (from the major MFGRs.)

http://www.dedacciai.com/products.asp?type=1&tid=64

http://www.columbustubi.com/eng/default.asp?pagina=4_3

http://www.eastonbike.com/tubesets_top.html

Basic summary - x number of well built aluminum bikes will weigh about the same, ride about the same and once painted, look about the same.