NO!SPEC: This came up with us just recently — two prospects wanted fairly significant parts of their projects done as part of the sales process.
The NO!SPEC campaign: Serves as a vehicle to unite those who support the notion that spec work devalues the potential of design and ultimately does a disservice to the client.
This is a good site, full of good information including lots of arguments you can respond with when someone asks you to do work for nothing.
We discussed this here before:
[…] you often get clients who want more and more information and more and more planning before they sign a sales agreement, until you find yourself putting far too much work into a sale which you haven’t gotten yet and might not end up getting.