I have collected Wikipedia-related graphs and charts in a single category: http://en.wikipedia.org/wiki/Category:Wikipedia_charts Please note that there is also http://commons.wikimedia.org/wiki/Category:Wikipedia_statistics where those files should be moved from the en-Wiki category, meta http://meta.wikimedia.org/wiki/Category:Wikipedia_statistics and similar categories on other WikiMedia wikis (and their subcategories...).
Next on my agenda is to go through every page in http://en.wikipedia.org/wiki/Category:Wikipedia_statistics and create a short table of content.