Good call Simon on Gang of Four's "Entertainment!", which completely rests on its bass line.
I was going to mention some Black Sabbath, Cream, and Grand Funk RR titles, but they've been covered so I'll second them.
The James Gang has some memorable bass lines, especially on "Rides Again" (Funk #49, The Bomber: Closet Queen, etc.)
The Melvins were the rare band that mastered overproduced 90's bass lines and turned them to their advantage, in large part by gleefully running things to an absurd extreme. "Stoner Witch" is their best example, especially with songs like "Queen" and "Revolve".
Of course hip-hop stands or falls, and usually falls, with its bass lines. But when it's good it can be very good; arrythmic, disjointed, impossible-to-dance-to lines that leave you shaking your head ("how did they make music from that?") can nonetheless produce some really terrific songs. Examples:
Cannibal Ox's "The Cold Vein" (especially "A B-Boy's Alpha" and "Raspberry Fields"),
El-P's "Fantastic Damage" ("Accidents Don't Happen" has a near-impossible bass line, but it comes together in a great track nonetheless).
Company Flow's "Funcrusher Plus"
Anti-Pop Consortium's "Arrythmia".