Thank them for the business, indicate what needs to be signed and what the next steps are.
1234, Main Street
Boston, MA 02123
08 April, 2005
<Recipient Address Goes Here>
We appreciate the opportunity to do business with you. Enclosed is the contract which outlines our agreement. <Instructions.>
Upon completion of the contracts, <next steps>. We look forward to doing business with you.
encl: <List of enclosed items goes here>