I don't really want to spend any money on it, but I do want something more functional than tattered and stained notebooks.
http://freemind.sourceforge.net/
The advantage with using the mind-map is that you've an easy way to categorise each entry, so it can include things you've researched, places you've created, with their own sub-details, other fictional language names etc etc and it's all fairly browsable.
see
http://freemind.sourceforge.net/wiki/index.php/Screenshots
Personally, I'm waiting for someone to create something like the above that uses the interface of the Visual Thesaurus... now *that* would be sweet.
http://www.visualthesaurus.com/
I've used wikispaces.com for some. They are useful (though I used mine for sharing the trip-planning tasks with a friend, who brings what, etc. not expressly for what you're talking about, but I think they'd fit.)