I am definatly saying Low. You just can't beat it. It takes a few listens to get used to the shear avuant-guarde-ness (is that a word?) of it but when you do, it is amazing. The other Berlin trilogy records are good as well (especially "Heroes") and the other recomended are:-
Station to Station
If you to like Low, I recommend Krautrock music, as that was the influence. Try Tangerine Dream for the instrumentals on the B-Side
and Harmonia for the vocal tracks on the A-Side.
Hans-Joachim Roedelius is also a good buy.