I contribute to the following wikis:
I tend to write my notes in Markdown (may just witch to org-mode at some point?), so being able to easily convert from that syntax to something I can plonk into a wiki is very useful! You can even grab HTNK files and stuff straight from the WWW.
MD to Doku
pandoc [inputfile.md] -f markdown -t dokuwiki -o [outputfile]