Station to Station. He was also working on the movie The Man Who Fell To Earth, Nicholas Roeg's film interpretation of the sci-fi novel by Walter Trevis, with Bowie acting and attempting to write a soundtrack in his L.A. home. But perhaps more about the movie anon, cos I haven't seen it for years.
The soundtrack idea was however abandoned and thus Station to Station came about. Or at least that's what seems to have happened since our David was so off his head all of the time that he remembers practically nothing of the period ("I know it was in LA because I've read it was"). Apparently it was at this time however that he started to take an interest in Krautrock, especially Kraftwerk, although to be honest not a lot of that transpires on this album.
A memorable live tour followed, for which Bowie had originally wanted Kraftwerk as support band. Sadly, this never happened for technical reasons.
Gary Numan (né Webb), who also denied said gesture. "All you need is some dickhead at a music paper or whatever to make an issue out it ...." said Bowie, which is exactly what the NME did.
Station to Station has recently been issued in a special triple CD set - original album remastered plus the legendary Nassau concert. Get it.