I don't know why this should spark any kind of debate. I can tell you the bikes that I find desirable, and Ebay prices reflect their desirability pretty well.
Colnago Master
Tommasini Prestige
Masi Gran Criterium
DeRosa Primato
Mondonico Diamond
Anything SLX, EL, EL OS, or a high quality Columbus tubing, imported by Ten Speed Drive. Guerciotti, Tommaso, Ciocc, Rossin.
As you can tell, I'm mostly into Italian bikes. I know there's a lot of nice stuff out there from all over the world, most of those don't excite me very much, aside from maybe a Waterford made Paramount from the late 80's / early 90's.