They are quite good.
Also most real estate agent websites have what is called an IDX link to the Multiple Listing Service. It's basically a consumer version of the MLS. Totally up to date.
The reason you won't see a complete grouping of all listings available on the MLS on any of these sites is that not all agents belong to these sites. The listings must be submitted by the agents who participate in these forums. They are not pulling data directly from whatever local MLS the way the real estate company websites are. I would suggest looking here:
Fina a Realtor and you wont be missing anything. That is why we are here.
If you are seeing anything from realtytrack (or other 7 day free trial foreclosure listings) forget them. Many do not really exist as a foreclosure. Certainly they are not for sale at the price listed.
Some of the listings you are viewing could be for sale by owner listings which are probably not listed in the MLS. If you connect with a local real estate buyer's agent they can set up a custom MLS search for you which will give you exposure to all properties listed with real estate brokers. To find for sale by owner properties I suggest you search website such as craigslist, your local newspaper classified ad websites, websites such as trulia and zillow, fsbo.com, forsalebyowner.com, etc.
This is one of those times I have to say, Team up with a Realtor. Local MLS in the Twincities can set up an automatic email with the properties you are looking for based on area. bedroom, bathrooms, sq ft, area, almost any, any feature you are looking for. Also, I am sure you would like to know if a property is a Traditional sale, a short sale, a property in foreclosure (redemtion period) or an REO (or foreclosed) property.
Take into consideration that Trulia, based on my expirience. has around 3 days delay from real MLS property active.
Zillow, I had notice in some cases, 7 days. So the information you are seeing, is "old".
What area are you looking for? Any personal reason no to team up with someone that will help and consult you on your next real estate investment?
Best on your purchase.