General Emulation and other Platforms:

ZX Spectrum [the infamous arch-enemy of the C64]
comp.sys.sinclairThe Major newsgroup for Spectrum fans, sort of a combination of c.s.c and c.e.c
The comp.sys.sinclair FAQThe best Spectrum links resource out there, and also lists every single Speccy emulator out there (including a C64 based one!)

BBC Micro [Home of Elite!]
The BBC LivesA brilliant site, which is home to a large emulators list in addition to a huge software archive

M.S.X
MSX.ORGOne heck of a good resource, with detailed lists on emulators, download sites and other stuff.
The MSX Emulator PageOne of the biggest MSX archives around, this has the titles divided up by MSX model, and lists by name too.
Multi-Platform Sites:
Dave's Video Game ClassicsOne of the best sites there is, although, one of the biggest victims of the IDSA, still containing a huge number of emulators for differing platforms.
Zophar's DomainThe other 'best emulation site', with also sections containing 'Homebrew' games and translation patches for console carts.
Anti-Emulation Sites:
The Interactive Digital Software AssociationThe people behind the whole emulation trouble. Need I say more?
The Campaign to Leave Emulation Alone [Plus an R]The major Anti-IDSA campaign online, this site lists permitted titles for distribution and members who do/don't support the IDSA action, and up-to date news over the crisis.