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/)
My favorite, that I just found yesterday in fact, is:

[PadMapper](http://www.padmapper.com/)

It automagically pulls in Craigslist, ForRent, Apartments.com & "Others". You can filter by price, size, bathrooms, bedrooms, whether they allow animals or not, pictures & more. 

It's based on Google Maps. Very handy. :)