Well, it depends on what you're looking for. I'd start with Another Green World, as it shows Eno at a crossroads between his pop and ambient work. Before and After Science shows this nicely as well, as does his work with David Bowie on Bowie's Low and Heroes (though I'd avoid Lodger, the third in Bowie's Berlin trilogy, unless you're a big Bowie fanatic).
As far as his more ambient works go, I'd recommend the experimental work Ambient 1: Music For Airports, Ambient 4: On Land, and a whole bunch of collaborations: the Fripp & Eno album Evening Star, the album with Harold Budd and Daniel Lanois called The Pearl the David Byrne & Eno album My Life in the Bush of Ghosts, and his work with Cluster (either the compilation Old Land or the self-titled Cluster & Eno will do fine). All these represent either concept approaches or novel collaborations in Eno's approach to reductive composition in the mid 70s to early 80s.
So I'm still on-topic, I bought a couple CDs this weekend:
Klaus Schulze - X
Silver Scooter & Super XX Man - "The Scot Garred Sampler"
Franciose Hardy - La Question
Jandek - Six and Six
The Stratford Five - A New Design for Living
Plus a lot of other stuff, but I can't remember what it is as I am at work and these are the only CDs from that trip that I have with me.
