Seety

Seety.co.uk offers a virtual tour of London's famous streets and landmarks. Described as a "tribute to the city we love", Seety map-makers spent the summer touring the city in a Volkswagen Golf mounted with a tripod and a camera.

From their website:

A couple of months ago, if it was a sunny day, or at least a not too cloudy one, you may have seen us around London while we were taking pictures: we were using a couple of Volkswagen Golf with a sort of tripod over it. Some of you have been shouting at us: "Look! A time machine!". If you are a police officer you may had a closer look at us, you have been checking our cars over and over again...
The goal was to map every single street - road - way - square - mews (you got the idea) of central London, and a bit further than that. Eventually we have recorded images for slightly more than 1000kms with a total of 171,103 pictures published on this site. Not all the streets matched our expected picture qualities, and we will probably refresh our database, hence, if you notice some of these streets, look for a car with a sort of tripod, it's most probably us!

There's nothing really magic or rocket science going on here, we just use consumer level electronics and some proprietary software. The picture acquisition is completely automated so a single operator can just focus on driving; he's able to map around 40 kms per day. After the initial acquisition phase we post process the pictures checking for privacy concerns and create the map that will give you the illusion of walking around the city from your pc.