A good old-fashioned website! It’s hope to information on the construction of a wide variety of console platforms! Docs on the NES, the Sega Master System, the PC Engine (a.k.a. Turbografx 16), the Mega Drive (a.k.a. Genesis), Gameboy, SNES, Saturn, Playstation, Virtual Boy (yes), Nintendo 64, Dreamcast, Playstation 2, GBA, Gamecube, Xbox, DS, PSP, Xbox 360, Playstation 3, Wii and Wii U.
The Copetti site: Architecture of Consoles