Lender help is here, this is a great breakdown on the qualifications from a local lender Matt Topping, take a look:

Salaried Borrowers:

Most recent W2, most recent paystub, most recent 30 day history on bank/brokerage, retirement accounts (all pages of the statements), copy of driver's license, copy of current mortgage statement, insurance, and tax bill on all properties owned. 

Self Employed Borrowers:

Most recent 2 year's personal and business tax returns (just federal, all pages, schedules, K-1's), year to date Profit and Loss statement, all other requirements same as Salaried Borrowers. 

Retired Borrowers:

Most recent 2 year's personal tax returns, most recent pension and social security award letters or 1099's, same requirements on other items as above

Miscellaneous

If your buyer is using rental income to qualify, we'll need the most recent 2 year's personal tax returns, as well as copies of the current leases. 

If someone has less than 25% ownership in a business, we'll only need the last 2 year's K-1's...if the ownership is 25% or more, we'll need the k-1's and the full tax returns 

Jumbo loans will require 60 day's worth of assets statements, as opposed to 30 days

If your buyer is divorced, we'll need the divorce decree...if they're using alimony/child support for income, we'll need 3 month's evidence it's been received, and that it will continue for at least 3 years.

If a property is being sold furnished, please write into the contract that the "furniture is being conveyed as a convenience and has no value".

 There are, of course, other things that may pop up that require further documentation (large deposits on a brokerage or bank statements, inquiries on credit reports, etc.), but I wanted to at least give you an idea of what banks are looking for in the current lending environment.  This is especially important if you've got buyers coming to town looking to put an offer in on a bank-owned property that requires a pre-approval.