Topic Maps is a Web 3.0 enabling technology: Creating rich semantic models. Browsing and searching faceted information. Integration from various data sources. Ultimate flexibilty. Enjoy!
Most regular public activity happens on mailing lists like TopicMapMail.
A German Mailing list is available on http://www.topicmaps.de/
The Twitter account for this web site is @topicmapsorg.
The @tmlab is quite active retweeting interesting articles and project announcements.
Many Topic Mappers are on LinkedIn, you can find some of them in the LinkedIn Topic Maps community group.
For programmers, many software libraries, called Topic Maps engines are available to use, some of which are part of complete knowledge management solutions.
Students and academics will find the Topic Maps Library useful. It includes many publications, a glossary, information about standards and more.
Many companies offer commercial services and/or consulting around Topic Maps products. The list of sponsors of TMRA is a good place to look for them. The Topic Maps Projects list gives some starting points, too.
The Standards are available through ISO. The latest versions can also be obtained at isotopicmaps.org. The most prominent standard is the Topic Maps Data Model which uses XTM 2 and CTM as serializations.