Even "lorem ipsum" will do. Read the words, sort them, unique them, and write them out sorted. Granted, it's not very useful (although as a student I once got paid for writing a program that reads a text and outputs all the words scrambled - you never know), but it has the chance to show some very basic idioms in any language you implement it in.
Heh... this occurred to me, if only to show off the C++ template metaprogramming version (object code size grows linearly with the number of bottles!).