Candidate Coding Project

I am looking for a good coding project to ask developer candidates to complete. 
I have tried a few scenarios in the past with mixed results and would like to actually
find something a little more interesting and usable.

How To Use The Test

1. Resume sort
2. Phone screen with the candidate (15-20 minutes)
3. Email the project to them
4. Receive the completed project ( or not – process over )
5. Examine the solution.  If we like it, proceed.
6. Invite the candidate in for face-to-face interview
7. Forward the solution to all interviewers
8. Candidate comes prepared to discuss the project for about 10 minutes of an hour long
   interview block

Test Ideas

1. Write a small app to manage an address book in XML format from my hard drive.
2. I dunno man, that’s the point of this post.

Leaving the implementation completely open to interpretation is the point of this
exercise.  What will they do?  Your suggestions must allow for a variety
of possible implementation.  It will be interesting to see if someone does a
command line application or windows app or what.