Ash Ra Tempel. I wouldn't think of the Scorpions as what the term Krautrock is traditionally used for, it seems to imply a bit of a progressive nature. But I do LOVE Scorpions.
Kraan and Can are real close also: Agitation Free (one of the key groups in the genre) Ash Ra Tempel and Ashra (at least their album Blackouts) Guru Guru (for craziness) Cosmic Jokers (a krautrock super group of sorts) Release Music Orchestra (kinda jazzy krautrock) Neu! (suprised no one mentioned them) Manuel Göttsching Krokodil (Swiss KR) Ikarus (lesser known, gem in the genre) Faust (no one mentioned them either??) Eiliff (especially for this one epic song) Cluster (I guess is KR?)
I'll have to go with Can, and with Amon Duul II and Faust close behind. I'm still exploring the genre though.