There are a lot of comics sites out there!  Here's my guide to
some of the best Marvel Comics Silver Age -related sites:

Links last checked, page last updated:   16 Oct 2004

Best Reference sites: The Grand Comics Database Project
Arthur Lee's Marvel Comics Reprints site

Markus Müller and Paulo Costa's "Unofficial Handbook of Marvel Comics Creators" / "Unofficial Handbook of Marvel Comics Creators" (yep, two sites, virtually identical, use which ever one loads faster for you)
Best Historical sites: Jamie Coville's The History of Superhero Comic Books
Don Markstein's TOONOPEDIA
Jess Nevins' History of Timely Comics
Blake Bell's The '50s ATLAS Cover Gallery
Best Capsule Reviews site: Jay Shayer's Comic Book Compendium
Best Daredevil sites: Kevin Hall's The Daredevil Resource
Kuljit Mithra's Daredevil: The Man Without Fear
Best Spider-Man site: Jon Couper's SpiderFan - the unofficial Spider-Man web page
...which includes the Peter Parker's Pad on-line magazine!
Best Fantastic Four site: Sean Kleefeld's FF Plaza
Best Avengers sites: Van Plexico's Avengers Assemble!
Avengers Forever
Best Dr Strange site: Erik Elzenaar's Dr Strange...Sorcerer Supreme! site
Best SHIELD site: Humberto M. Ferre's Nick Fury, Agent of SHIELD page
Best Iron Man sites: Advanced Iron
Dave Huber's Iron Man Review Guide
Best (and only?) Thor site: Matt Hoxsie, Paulo Pereria & Carl Reno's The Mighty Thor site
Best X-Men site: Eric J. Moreels' X-Fan
Most off-beat site: The Wondrous WASP! (in English and Italian!)
Best Artist-related sites: Blake Bell's Ditko Looked Up
Gene Colan's Virtual Studio
The Jack Kirby Collector
Tony Robertson & Erkki Rautio's Steranko site
Best general Comics-related site: Jonah Weiland's Comic Book Resources
Best original Comics-related site: Chris Kohler's Captain Relhok's Comics pages
(once a cover gallery, now a showcase for Chris's own work - impressive, it must be said)

Special mention:
The One, The Only: Cheeks, The Toy Wonder's Homepage
(...currently without images but all the text is there)
The Other One, The Only: Mister Meesh's Comics of the 1980s Homepage
(...truly in the spirit of the dear departed Cheeks)
Another promising 1980s site: Jay Shayer's Marvel Comics of the 1980s
Best non-Marvel cover galleries: Mike Costa's EC Sci-Fi covers
Doug Gilford's MAD Cover Site
(...that's MAD Magazine, if you were wondering)
European-language Marvel:
Germany: Gernot Zipperling's German Marvel Comics site
Bart Bethlehem's HIT Comics Project
Netherlands: Bart Bethlehem's HIP Comics Project