The new balance

I don't know what everyone is using for looking up addresses, but I normally use PostcodeAnywhere's demo. They allow five free searches a day, but now I'm going to the source of this information: I've found an equally fast service from no less than the Universal Postal Union: Address Doctor. It's international and lets you search with just a house number and postcode, or with whatever information you have. Sometimes I visit a customer and I know the street address but need the postcode for invoice purposes, so this is going in my bookmarks straight away and there's no usage limit. Any better suggestions?

UPDATE

Ah, it is limited after all. I've noticed that the congestion charging page on http://tfl.gov.uk lets you look up a postcode, then presents you with matching addresses. That's very handy, too, but only if you already have the postcode, obviously.