I found this thread to be a good resource for information on the Prequels from around the time of release (+ some SE content):

Phil Tippett on the Special Editions: “They’re shit” + £2b for George to direct the Prequels

It has a number of articles written about the Prequels at the time of release, the deals and tie-ins (PepsiCo + many others), the hype and anticipation around TPM, the merchandising, and also some YouTube videos of note about the PT over time.

A good read through the Prequel Trilogy section of An Index & Help Thread for Beyond the Original Trilogy also turned up some cool information, sources and discussions.

The Secret History of Star Wars book, and the website for the book also features some great explanatory and revealing Prequel Trilogy content (I really need to re-read the book again). Especially these two TSHoSW articles:

The Beginning: A Look at the Rough Draft of Episode I

The Turn: A History of the Evolution of Anakin’s Downfall

Pre-PT era lore | an OT & EU scrapbook resource | additional info & sources welcome is a great reminder that George changed some 20-30 years of previously established Star Wars lore and material for his much changed Prequel Trilogy.