Pre-approval with the bank who owns the home:
When making an offer on a REO home it is to your advantage to be pre-approved with the bank that owns the home. When making an offer on a home having a pre-approval letter from the bank who owns the home will increase your chances of beating a competing offer from a buyer with the same offer or even slightly higher without.

The problem with getting pre-approved once you see the house you like is that it takes time for the approval process, about 3-5 days average. So it is best to get cross qualified with a few of the different major banks in your area before hand. The advantage is that you will be able to get preference with any bank which you qualify with. Also you will be able to shop the different banks to get your best terms and rate. Since most of the listing are either Wells Fargo or Homesteps and Homepath, or fannie and freddie. I recommend to buyers to get qualified with all three. Most of the smaller banks also prefer to at least see a known institutional lender. I recommend starting with Wells Fargo, then go from there.

Different websites which list homes by bank:

All of the different banks who sell homes as foreclosures have their own websites which list the homes they own. Below is a list of the different websites banks have set up to preview their homes. Its a good idea to check out what homes are available for the bank you are planning on doing business with.