Here you will find useful sites containing tools and resources for Simutrans.
Many of the resources below are created by fans. As with all things Simutrans-related, anything not released by the development team (the newest versions of the Simutrans engine/executable, and generally Pak64, which is the assumed and official Simutrans graphics set) may not be kept up to date with the latest version.
The entire community is made up of volunteers; folks making these programs can't add the latest version until it is released, and even then, everyone has a 'real' life - updates are never immediate. But often, they are kept pretty well up-to-date. But you should make sure that they support the particular version of Simutrans you have downloaded.
Simutrans.com - Links
:arrow: http://www.simutrans.com/links.htm
(credits to Isaac for original text)
EDIT: Now all links are at www.simutrans.com.
I started a Simutrans group on Facebook:
http://www.facebook.com/group.php?gid=83052149546
I removed that huge list of sites. Now you can find (almost) everything by simutrans.com. :)
Plus, I'll add Simutrans' Facebook into Simutrans' sites list.