Here is a roundup of recently found Google Maps mashups and overlays..
Washington DC Metro Map - Yet another Washington DC Metro Map (the third one I've come across..) [via]
BBC London JamCams - locations of the BBC's traffic cameras throughout the city of London, England.
San Francisco Schools Information Map - Here is a map which displays information about all schools in San Francisco.
Nuit Blanche Map (Paris) - Although the event has just passed this weekend, Nuit Blanche is an event in Paris which lasts from 7pm until 7am the night after on Oct. 2nd. This map showed locations of the non-city-sponsored venues for people taking in the event.
Google Stalk (Canada) - Helps you plot people by Canadian telephone number.