This luminous, foot-high jellyfish tank (with real fake jellyfish) is intended as a desk-accessory; it cycles through different colored LEDs and costs $120 or so.
(via Gizmodo)
Update: Phil sez, "It's not likely that a setup like that would allow the jellyfish to live more than a month or two (if that). A proper environment for jellyfish would require a much more expensive setup than can be obtained for $120 – more like $1200. Living things should not be abused for entertainment in some desktop executive toy."
Update: Bill sez, "the jellyfish tank has silicone jellyfish in it, not live jellyfish. (Which is a shame, as I've always wanted a pet jellyfish.) Google translate of the source page confirms."