Google Maps Mania has a post on the earliest maps of London. First, the Copperplate Map (ca. 1550s) of which no prints survive: only three copper printing plates, out of 15, are known to exist, two of which are held by the Museum of London. On the other hand, the Agas Map (above), which appears to be a close copy of the Copperplate, is available in an online interactive version.