Shot these recently at the Vancouver (BC) Aquarium, a few more more here. Always tough shooting in the dark and through glass, but would love to see other jellyfish photos, and would welcome any hints that you have found helpful in shooting or processing.
Taken at the Monterey Bay Aquarium. Full gallery at http://www.pbase.com/trinko/jellyfish Note that the third image is actually a stop motion movie showing two jellyfish getting untangled.