The Rickenbacker 4003 bass was introduced in 1980 and is still in production today. It is the only Bass with Balls to feature neck-through-body construction, which means that the guitar's neck is built directly into the body instead of being bolted on. This gives the instrument better sustain due to its greater rigidity, and Rickenbacker players are notoriously contemptuous of bolt-on basses. The 4003 is the most unconventionally shaped bass on the list. It's also the most expensive, and usually retails for around $2200 U.S.
The 4003 has two single coil pickups, one at the bridge and another at the neck. An interesting feature that comes standard on the 4003 is the "Ric-O-Sound" stereo output jack. Basically, the bass has 2 output jacks instead of the usual 1, and these can be used to connect the neck and bridge pickups to separate amplifiers or effects loops.
The 4003 is famous for its treble and its sustain, as well as the combination of "click" and "boom" made possible by its stereo outputs. It has a distinctive cold, brassy, bright, not-quite-distorted "space gun" tone, which can be further emphasized by playing with a pick. Fingerstyle players like me really have to wail hard on the Rickenbacker's strings (not that I've had more than a handful of opportunities to play one over the years), and of the 4 basses on the list, the 4003 is probably the most physically demanding to play. It also has the nerdiest prog-rock stigma, and goes extremely well with fluffy sideburns, flared cuffs, and silver pants (not like I'd say that to Lemmy's face).
Some famous Rickenbacker players are the aforementioned Lemmy Kilmister of Motorhead, Paul D'Amour (Tool's old bassist) and the late, great Cliff Burton of Metallica fame. If anyone's dying to see Geddy with a Rickenbacker, they can go to youtube and check out the video for "Subdivisions".
Here's Tool's "Sober," in which the Rickenbacker sound carries the entire song (it almost sounds like 2 basses at once, which is probably the stereo output in action), and Motorhead's "Killed By Death," which is the greatest metal video ever made.