Mining mythology and legend seems like a source for a few. Asgard, Valhalla (drinking hall of the glorious dead), Midgard (that's Earth to the Norse - actually means "middle earth"), Olympus, Shangri-La, Avalon, Hy-Brazil, Atlantis, Camelot.
And let's see, from fiction in general: Oz, The Emerald City, Kandor (Superman's bottled city), Lankhmar (Fafard and Grey Mouser), Neverland (the kid's table?), Wonderland, Hyboria (Conan), Barsoom (John Carter of Mars), Pyrdain (The Book of Three, also an old name for Wales), The Bazaar on Deva (MythAdventures), Melniboné (Elric), Earthsea, Stormhold (Stardust), Narnia.
And of course tons of places from the Lord of the Rings - I won't even start. I could also go on about The Song of Ice and Fire, or even Harry Potter.