Ed Chin - RealtyTrac is one I can think of....

Doesn't your mls list them? Contact lenders if not

There should be a foreclosures category in your MLS.

Go to the local foreclosures sales.

I do not look for properties not listed in mls as buyers do not pay me the fees. 

Our mls has foreclosure information, but somehow I've managed to avoid foreclosures and short sales.

Foreclosure radar

Our MLS has a refined search where you can see only bank owned homes that are listed. The county trustee site also lists the homes that are in varies stages of the foreclosure process, so you can see what will be coming on the market in the future. 

There are many down payment assistant programs for people that qualify depending on your city or state. 

Your MLS.  NOD, Foreclosure.

As others have stated - the multiple listing service for those already listed as well as RealtyTrac(not really useful in my opinion).   It's not an area of business that I have found worth pursuing especially in the current market. 

My MLS has a REO category for listings.  There are online resources that have already been mentioned in comments here. 

PropertyRadar (formerly known as ForeclosureRadar) works well

Not as many anymore but MLS has them here

MLS, and court house are good placed to start.

MLS

Clerk of Court

In my market, there are several Brokers who handle the REOs that are for sale (one Broker works with HUD, another with Freddie Mac, another with local banks, etc.).   If you have Brokers like that in your local market, get on their email or notification list.

Most are handled by third party firms who list them in the MLS.

My market's foreclosure sales are almost non-existant so I pay no attention. Foreclosures are all listed in our mls and they are no bargain these days.

Unless you are listing them, the choices are the MLS or building relationships with those that do list REO homes. 

parked and reading...

I have seen plenty of scams out there ready to sell this info, but I suspect that it is not that accurate anyway.

One thing that I have found with foreclosures though is it takes time for the owners of them to see the importance of reducing the price to a level that the professional fixers to buy them.  Those who buy them too quickly generally pay too much and then end up being the next losers on these properties.

Not worth it to pay subscription fees to be the first in line to bid on these, the deals will come with time.

The local papers have a good list once a week here.

There should be a local service that is paid to give you this list.

Although foreclosures are a legally available means in my jurisdiction, they are not used frequently.  Power of sale is a more commonly used method due to various advantages for certain parties.  The MLS is one great source.