With the prospect of a Ghostbusters 3 looking less and less likely, Ghostheads wanting more from the boys in grey do have one option; 2009's Ghostbusters: The Video Game.
Technically, Ghostbusters: The Video Game IS "Ghostbusters 3". Taking placing two years after Ghostbusters 2, the game brings the voice talents of the original cast and fits well within the mythology of the original film, going so far as actually extending it.
You're not really into gaming you say? Don't worry. Ghostbusters fan Timothy Belanger, took it upon himself to recut the game into a full length, watchable movie. You can watch the first half of the 2 hour, 40 minute "film" above and the second half after the break.