I'm adding Glottopedia - a linguistics sort-of-wiki - to the links bar. I qualify with sort-of because Glottopedia has a couple of features that distinguish it from canonical wikis: first, not everyone can edit it - you need to have a good linguistics background; and second, it doesn't aim at total accessibility to the lay reader.
It's pretty embryonic right now, but it looks like it would be a good reference for people starting research on a topic. For example, I stumbled upon it while looking for resources on the semantics of infinitives in English, and the page on infinitive verbs looks like it will be helpful.
Surprisingly, I was unable to find a general law wiki when I searched for one.