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/)
Here in Aus I've always used the traditional [domain.com.au](http://domain.com.au) and [realestate.com.au](http://realestate.com.au). They're not super good, but they're always adding more features. They've got everything that [rchern](https://webapps.stackexchange.com/questions/1685/web-applications-to-look-for-rental-apartment-houses/1717#1717) mentions. I find the map view the handiest of the lot.

A new one launched a couple of weeks ago - [tenancyone.com.au](http://tenancyone.com.au/). I've not used it yet, but the basic idea sound good. You create a "profile" (I don't know what that entails) and they provide "tools" (once again, haven't looked closely). Their drawcard is they let the realestate agents find you, rather than the other way around, which is a novel way of looking at it.