I use Wikipedia all the time, and I might have been on my fifth visit of the day, when I clicked on the message at the top of the site asking for contributions to keep it going. What's Wikipedia worth to me? It is exhaustive, free from commercials, edited cooperatively, and free to anyone who wants to know just about anything. I made a contribution today (it's tax-deductible), and so can you. There's a little button over at the sidebar on the right.
You can read about their campaign (which started yesterday) here.