Question: This question may be interpreted as "too localized", but it is not.

I'm interested in what you find to be the best sites for this type of operation, regardless of where they are located. For instance, I want to learn about how do these sites do the following:

* How do they work with geographic information?
* What search parameters do they use?
* Can you personalize your search? How?

and so on...

Answer: 
The ones I've had most sucess with is:

* [Rightmove](http://www.rightmove.co.uk/)
Gotta go with [PadMapper.com](http://www.padmapper.com/). It aggregates lots of sources, offers lots of filters, lets you hide/favorite listings, lets you subscribe to updates to your search via email, and even has an iPhone app. And it's all map based, as the name suggests :-)