The Mordheim community might not be as big as it once was. However there is still a small, active community spread around the globe. Here is a short list of my 'go to' websites for Mordheim.
Tom's Boring Mordheim Forum
This forum is the primary Mordheim forum out there. It was created by many of the participants from the old Specialist Games forum that used to be hosted by Games Workshop after it was shut down unexpectedly. It is an excellent location to discuss rules, find new material, read battle reports and share photos of painting and modelling.
This is the website for the gaming group who are creating the upcoming Mutiny in Marienburg suppliment to Mordheim. MiM is the largest, most ambitious fan-made expansion so far and has been many years in the making. The primary author, Stuart Cresswell (Werekin) has participated in previous fan-made material such as the Border Town Burning suppliment and the Nemesis Crown suppliment. Unfortunately the rules are not available in a central location so you will need to comb through the blog posts to find all of the material.
Border Town Burning
This is the website for the Border Town Burning suppliment created by Christian Templin (Cianty). This high quality material allows groups to run campaigns in the distant lands of Cathay. The material is compatible with Mordheim campaigns set in any other location though. The quality of the material is too high to be overlooked by any serious gaming group.
The Mordheimer Information Centre
The Mordheimer Information Centre (more commonly known as just the Mordheimer web site) is a key resource for much of the material that was released by Games Workshop. A highlight is the master scenario list which contains rules for hundreds of scenarios. The home page is messy these days with an embedded Mordheim web ring banner so I now access the site via the Table of Contents.
This web site is home to a collection of fan-made material by the once prolific post Dave Joria (Styrofoam King). The highlight of this web site is his Sartosa suppliment for playing a pirate themed Mordheim campaign.
This web site contains the rules for the Nemesis Crown suppliment. Nemesis Crown was a global campaign run by Games Workshop for Warhammer Fantasy. A small group of fans led by Ian Davies including Stu Cresswell and Christian Templin created this Mordheim suppliment to allow Mordheim gamers to also participate within the global campaign.
The Specialist Arms website was an attempt by some fans close to Games Workshop to not lose the Mordheim community after the old Specialist Games forum was shut down. It hosts all of the Fanatic e-zine editions that were released by Games Workshop containing many fan-made Mordheim rules (and fan-made material for other Specialist Games such as Blood Bowl).
This is the web site for the original rules of the Khemri suppliment that was released in Town Cryer. Games Workshop made quite a few changes when they published Khemri in Town Cryer and not all were positive. This is a useful resource to have alongside the content from the Town Cryer.
Mordheim Revival Project
This is a website to keep an eye on. It has been created by Tom Bell (Brahm Tazoul) who used to be one of the Answer Mods for Mordheim and who released the Letters of the Damned e-zine for Mordheim. There is a promise that the Letters of the Damned may resume so hopefully the fresh, new material that is being promised will be released.
Mordheim Yahoo Group
This email group has existed since before the Mordheim box set was released. It is no longer active but is an archive of old material if you ever wanted to go searching. It also contains a lot of the PDF files that were released by Games Workshop from Town Cryer and Fanatic.
This is a selection that quickly came to mind when thinking of Mordheim material that is out there. If there is something that I have missed then please add a comment to let me know.