My favorite bass sound would have to be the doubled (or tripled?) line on God Only Knows. Rich, full, rounded tone, lots of lows and low mids, with some treble bite from the picked Fender part. A very simple part, not only complements the tune perfectly, but adds "weight" when that E/F#/G refrain comes in.
I could also make an argument for Jamerson's work on Side 1 of What's Going On (or Babbitt's on Side 2!)
EDIT: Quick appreciation for the arrangements of Brian Wilson. One of the reasons I dig the bass parts in his compositions is he really understands sonic space, giving the bass its own territory to work with. Especially for popular music at that time, the bass was much more prominently displayed than in a lot of other stuff coming out of LA at the time. That plus the great players he hired and the lovely counter melodies he'd write for it, it's what solidified my love for holding down the low end.
Which brings us to Joe Osborne's contribution to The Way Bass Should Sound.
Too many examples to list!