Krautrock is some of my favorite music ever. Here's a simplistic guide by your criteria.
Neu!— Neu! 1, 2, '75
Michael Rother—Sterntaler, Flammende Herzen, Katzenmusik
La Dusseldorf s/t
Early Kraftwerk (like Ralf und Florian)
Musik von Harmonia (the one with the detergent bottle on it)
Cluster & Eno
Popol Vuh—In the Garden of Pharao
Hans-Joachim Roedelius—Wenn der Sudwind Weht
Ashra—New Age of Earth
Manuel Göttsching—Dream and Desire
Early Tangerine Dream (like Atem
Early Klaus Schulze
If you don't like freak-rock, stay away from Ash Ra Tempel, Amon Duul II, Agitation Free, Guru Guru, Faust's first three albums, and stuff on the Cosmic Couriers imprint.
Can, to me, are a separate entity from all the other groups here. In my opinion, you can't go wrong with their first five albums. After that, things get a little dicey. I'd consider them more like a post-punk band before there was even such a thing as punk. My personal favorite's Monster Movie. The double-CD set called Anthology is a good cross-section.