Five top short yet deep novels

At The Barnes & Noble Book Blog Joel Cunningham tagged "five great books short enough to polish off in an afternoon, but deep enough to keep you thinking long into the night," including:
Slaughterhouse-Five, by Kurt Vonnegut (49,459 words):

Vonnegut’s masterwork packs more ideas—time travel, gender politics, a potent antiwar allegory, er, aliens putting people on display in zoos—than most novels