Sites that have great retro-computing/gaming resources
Retro Commodore - Carsten's fabulous C64/Amiga resource. Plenty of great scans of manuals/mags and books for Commodore's home computer range of products.
Retromags - I call it a sister site for retro magazines with a heavy emphasis on USA titles.
Out of Print Archive - another resource for magazines. While output is not high, you cannot fault the quality of their releases :-)