We've used realtor.com for lots of research, but a lot of times those listings are outdated. They just don't get updated as quickly as they should. Also, we've noticed, the houses usually seem WAY better online than they did in person. Not that they were misrepresented, just gave an over flattering view/description.
Forsalebyowner.com can get you lots of information on houses that aren't through the MLS listings. We listed our last house that way, and got some hits from it, but ended up selling it locally only 4 days after we put it on the market, so I can't really tell you how good the website was. We have looked at a few houses there just for information though.
Most of the real estate companies have websites. Just type in the name (i.e. Century 21, Caldwell Banker, etc.) and then it will let you search by area. We've found LOTS of information that way. Way more reliable than realtor.com since it's updates when the MLS is updated. Meaning if there's a contract on it, it will show that on the website.
Didn't mean to be so long! We've bought & sold 3 houses in the past 2 years due to multi-state moves, so we've done a lot of our research/looking on the net. Good luck with your home buying and selling!