I've listened to Jethro Tull's "Benefit" album and always liked the song "Inside," but it wasn't until last night that I realized that it has an amazing bass line. It carries the whole song, and it totally sings with Ian Anderson, it's like another vocal line, but very rhythmic.
I recommend hearing a hi fi version to get a feel for the bassline, but here's this:
http://www.youtube.com/watch?v=daEXzsrJAoU
Kudos to Glenn Cornick for some amazing playing.
I've never thought of a bassline as being my favorite, but this is it for me right now. It's not flashy, it just fits everything so perfect.