The website MacMerc.com today published a list of products that are due to enter more specifically on March 17 for Apple's “classic and obsolete” list. Its last update was made on December 8, 2008.
The "classics" (not to say "old"), following California (USA) laws that mandate the maintenance of spare parts inventories, include Xserve RAID, Xserve (Slot Load) and Xserve (Cluster Node).
The rest of them are already considered “obsolete”: PowerBook G4, Power Mac G4 (Digital Audio), Power Mac G4 (Quicksilver), Macintosh Server G4 (Digital Audio) and Macintosh Server G4 (Quicksilver).
Regardless of any classification, I am sure that such products certainly contributed to the work of many people if they do not do so today, right?