donation@wikipedia.org is the correct email address to use.
I think that's all you need to know.
Tomorrow I will set up a web page on wikimedia.org (the foundation website) with a variety of buttons and what-not to use, but there's no reason you can't get started now if you like. At least initially, all funds will go towards the new server(s) that I'm shopping for -- the more you give, the more you get. :-)
Also, I'm talking to a few different merchant account processors, so that we can get our own merchant account and save on fees. But via PayPal, we can accept money already via credit card, and in U.S., Canadian, Euros, Pounds Sterling, and Yen.
Although it isn't as full global as I would like, Paypal is available to people in the United States and 38 countries, including:
* Anguilla * Argentina * Australia * Austria * Belgium * Brazil * Canada * Chile * China * Costa Rica * Denmark * Dominican Republic * Finland * France * Germany * Greece * Hong Kong * Iceland * India * Ireland * Israel * Italy * Jamaica * Japan * Luxembourg * Mexico * Netherlands * New Zealand * Norway * Portugal * Singapore * South Korea * Spain * Sweden * Switzerland * Taiwan * United Kingdom