If you have a business you'd like to sell at some point in the future or are even considering starting your first business you've got to check out 'Built to Sell: Creating a business that can thrive without you' by John Warrillow (affiliate link).
The title says it all and it provides a road map for creating a valuable sellable business. I first found about about this book by following John on Twitter and it's a great companion book to Michael Gerber's 'E-Myth' series.
John says:
"You should always run a company as if it will last forever, and yet you should also strive constantly to maximize its value, building in the qualities that allow it to be sold at any moment for the highest price buyers are paying for businesses like yours."
It's one of my favourite books of the year so far.
[youtube=http://www.youtube.com/watch?v=k-eu7EZUTwM]