Following a recommendation from Heather, I've taken a look at the wikibooks Japanese course. The kanji lists are good, in that they are structured around the levels defined in the Japanese Language Proficiency Test. As with Wikipedia, the content is provided by ordinary bods like us, so there are gaps and no doubt the possibility of errors. If we all threw our best efforts at this, it would no doubt be very worthwhile - both for the result, and for the benefit we would gain from putting the effort in. So I had a go at adding examples to some of the kanji sheets, and picked up some new compounds in the process.

My favourite online resource for 漢字 is zhongwen.com, an online 'genealogy and dictionary' of Chinese characters. The content is vast, and you can click on any character within any of the compounds or genealogical tables, to go to the page for that character. I don't know if anything similar exists for Japanese.