Now, now. Carolyn asked about Pre-Foreclosures; I'm sure she knows the property is not technically for sale and may NEVER be for sale if the borrower is able to get loan modification or bring their payments current.
Carolyn, the following website is from HUD. It has links to homes for sale by the U.S. Marshals, the IRS, and others. Many of these properties come with hazards and liens attached, so I do highly recommend working with an Agent if you plan on purchasing one of these.
When a home has finished the foreclosure process and is actually owned by the bank, it is typically listed on the MLS and any Realtor (or Realtor.com) can provide those.