I first encountered the idea of the Memory Palace in Jonathan Spence's The Memory Palace of Matteo Ricci [1984] (Ricci was a 16th century Jesuit in China), and saw a visualization of the mnemonic technique in one of the episodes of James Burke's The Day the Universe Changed. Frances Yates' The Art of Memory [1966] provides a marvelous history of the technique, and it still finds resonance in a number of web documents.
The art of memory was a necessity before the era of cheap paper and printing. To a Greek or Roman orator, memory was power, and the most powerful memory techniques were spatial. The ancient technique of spatial memory is surprisingly straightforward. One systematically plants memory objects in memory locations along a familiar route that can be visited in the mind's eye. Later, these objects are recalled in sequence, forward or backwards, as one mentally revisits the route. Precise instructions for constructing a personal memory palace appear in three classical sources: Ad Herrennium (anonymous), Quintilian's Insitutio oratorio, and Cicero's De Oratorio.

(from Muir and O'Neil The Architecture of Digital Space)

Here are some links to Memory Palace implementations and writings:

The Collective Memory Palace (Serena Lin)

Artificial Memory: Mnemonic Writing in the New Media (Tim McLaughlin) [seems to be dead link]

In the Palaces of Memory (George Johnson)

The Galileo Project