Have you ever wondered which is bigger -- Battlestar Galactica, or Battlestar Pegasus? And how do those compare to Deep Space 9? How do those compare to the crazy alien craft in Independence Day (officially named City Destroyers, apparently)? Well, all these nerd questions are now answered by the Sci-Fi Starship Size Comparison Chart! Now I finally have data to back up my, uh, "thought experiments" about how many Battlestar Galacticas it would take to destroy the Borg.
Taking things a step further, check out the Starship Dimensions site, which includes some additional comparison points -- from Dr. Who's Tardis (listed as 3 meters high), to the Imperial AT-AT walker listed at approximately 20 meters high -- the site includes the note: "The 15.5m height stated at StarWars.com just doesn't add up when you watch the movie." There's also a nice comparison under the "-2x" tab that shows relative dimensions of Godzilla (100m high), the Stay Puft Marshmallow Man (43m high), and King Kong (12.5m high -- "approximate").
And if that hasn't sated your sci-fi size comparison needs, check out the Starship Schematics Database, "dedicated to the sole purpose of archiving every single starship design ever conceived in the Star Trek, Battlestar Galactica, Babylon 5, and Space Battleship Yamato (A.K.A. Star Blazers in the USA) Universes, both official and unofficial, interesting and mediocre." Awesome. (Seriously -- check out the Battlestar Galactica Colonial Vessels section.)