The number of sites devoted to pens is now huge. Some useful sites are maintained by clubs and are listed under that heading. Most sites, however, belong to individual pen enthusiasts, and as one might expect, are a somewhat mixed bag. Historical information is nearly always taken from other sources, and usually contains more than a few errors; links to other sites, however, are often quite up-to-date, along with information on shows, local club meetings, and online chat sessions.
Internet Pen Resources: Craig Lewis has been compiling encyclopedic lists of pen resources online for some time, and now Tamer Oszu has put them on his website. If you can't find it here, it probably isn't to be found.
Rick Conner's Penspotters (formerly Penoply): Nicely laid-out and entertaining, much good basic vintage fountain pen info oriented towards the user-collector.
Pier Gustafson's: Home page of the celebrated artist, calligrapher, and stylophile; take a look here for samples of some of the most imaginative and attractive business cards you've ever seen, along with many examples of Pier's distinctively anthropomorphic pen renditions.
Bill Acker's: Thumbnail histories of selected pen companies, pictures, pen show information, links.