Be prepared to provide verification of income (including a pay stub and recent tax returns), bank account numbers and details on your long-term debt (credit cards, auto loans, child support, etc.). If you're self-employed you may also be required to provide financial statements for your business.
In recent years, lenders have been required to obtain more specific information from borrowers in order to package and sell loans to investors. If you were lending someone such a large amount of money, you'd want detailed financial information.