Many of you will know these sites already, but they may be helpful to others.
Sites I refer to all the time for pen identification:
For Burnham pens:
http://www.pengrauncher.co.uk/
For Swan pens:
http://www.mabietoddpenlists.co.uk/index.html
For Conway Stewart pens:
http://jonathandonahaye.conwaystewart.info/index.html
For Summit and other Langs pens:
http://www.summit.ch944.net/index.php
For Parker pens:
http://parkerpens.net/
For American pens:
http://www.richardspens.com/
Other sites
For a most entertaining and informative blog:
http://munsonpens.wordpress.com/
For pen discussion:
http://fountainpenboard.com/forum/
http://fpgeeks.com/forum/forum.php
http://www.pentrace.net/mboard.htm
There’s also
http://www.fountainpennetwork.com/forum/
I don’t go there, but to each his own.
For UK pen repair:
http://eckiethump.webs.com/
For nib work and USA pen repair:
http://gregminuskin.com/
For pen repair tools and supplies:
http://cathedralpens.co.uk/
That’s a start. Tell me your most useful pen URLs.
Goodwriterspens's Blog 
Very useful compendium, Deb. Thanks.
Various suggested additions off the top of my head:
John Sorowka – the UK-based nibwright: don’t think he has a website, but he’s Oxonian on FPN
Pure Pens in south Wales for custom Pelikan nib re-grinds
History of Pelikan pens: http://www.thepenguinpen.com/pelikan/pelikan_history.jsp
No, John doesn’t have a website and he’s not much in FPN either, unless he’s returned since I pulled out of FPN. The Pelikan site is a good one.
I just read that Pentrace is shutting down. http://members3.boardhost.com/PenMarket/msg/1391440713.top
Philip
That’s sad. I was never a member but I read Pentrace regularly.
Hi Deb,
Thank you very much for publishing the links to the various websites. That is very useful to me as I was not aware of a couple of the UK pen sites.
Kind regards,
Rui
You’re very welcome, Rui. If any others occur to me or come along I’ll post them too.
Deb –
David Nishimura’s blog: vintagepensblog.blogspot.com is one I read regularly.
Also, for those with any interest in Japanese writing instruments, (“Bruno Taut’s) cronicas estilograficas is informative.
Paul
Thank you, Paul.
May I update my previous response to also add the penboard.de web sales site. Tom Westerich and friends always tell us a good bit about the history of the pens offered, but often great stuff about the folks who made it. Today, for instance, I learned that the early Montblanc made pens for the Faber family and for Staedtler – things I had not known previously.
Thanks again, Paul. I’ll make up another post when there are sufficient URLs.