Good base for scanned sega materials - segaretro. I know, Kitsunebi don't like them for stealing magazines, but they have a lot of other good scans - ads, posters, manuals, maps and other... Plus, they started similar base for the NEC consoles... Many scans are in HQ.
For NIntendo - http://www.nintandbox.net - covers, labels, some manuals... Many of them in HQ.
Many scans can be found on forums like AtariAge...
TOSEC-PIX - old collection but with some-all-in-one-place materials
I have huge amount of links to different portals at home, but now i'm on vacation on Cyprus without access to them...
P.S. For manuals - look at my DMC collection))) Torrent can be found at pleasuredome.org.uk