There are producers who are more influencial, or more impressive from a perspective of craft, but in terms of thinking "ooh, this album is produced by X, I should check it out", my favourite will always be John Cale. The man did treportedly did most of the arrangements for the first two VU records, and produced the debut records by the Stooges, Patti Smith and the Modern Lovers, in addition to doing pretty much all the production, arranging and instrumentation on a lot of Nico's best stuff, and some fantastic solo stuff. Can't beat that.
