I have an old Bass Collection 4-string, from back in the early 90's. Seriously, it's insanely light. If it was the 5-string version on sale, I would have snapped it up by now.
It sounds pretty fat, considering and also has one of the slimmest and fastest necks out there.
Next, I'd say the Ibanez SR range are pretty light - not quite up there with Bass Collection, but a lot lighter than most.