Abarat by Clive Barker
Faerie Wars by Herbie Brennan
The Supernaturalist by Eoin Colfer
Ingo by Helen Dunmore
Kingdoms of Light by Alan Dean Foster
Neverwhere by Neil Gaiman, Stardust, too. American Gods if you want a challenge.
Glory Road by Robert Heinlein
Stravaganza City of Masks by Mary Hoffman
Owlflight and Joust by Mercedes Lackey
Through the Wolf's Eyes by Jane Lindskold
Dragonhaven and The Blue Sword by Robin McKinley
The Lighthouse Land by Adrian McKinty
Lord Loss by Darren Shan
Everlost by Neal Shusterman
The Secret Hour by Scott Westerfeld
Instead of just putting down different realm/time/planet thing, I just put down all the books that I could think of where the main character is dropped into a different culture/situation/whatever where he or she has to adapt fast.
Oh, and the webcomic Digger by Ursula Vernon fits, too. You can find it at diggercomic.com