not sure where you are looking to buy a new home but I know a great realtor in Santa Barbara..

A good one I know of is the one below. The other sites folks mentioned are good but this one has a call back feature and email feature where, if you see something you like and want more info, you click it and you get an email from the agent or seller who is selling it or even a call back if you want to speak to a live person.

Also there are free pdf forms and reports to download.

Many sites I’ve seen make you fill in a form then you have to wait for someone to call you back or email you but this one shows everything live on screen instantly. I like that better as I don’t like waiting for things.

Definitely, realtor.com. This offers you the option of search anywhere for the most part.
Also, if you go to major realtor companies websites you can search their listings often the same way by state and some are even international.
Example just search Keller Williams, Prudential sites.

Zillow is the best thing I’ve seen so far (i’ve been looking for land and houses across the US.)

Great ability to look up the price of houses in an area, or you can pick a specific house and get many more details.

Yahoo Real Estate is a very good site with no pressure. Easy to look around.

realtor.com and my fav, is landvest.com, it is only northeast listings but all multi-million dollar homes with plenty of pictures!

If you happen to live in the San Francisco Bay area use

Realtor.com is a good place to get started.

zillow.com stinks for values , but the aerial pics are really great