I have different reasoning than the parent commenter. Why do you want to help fund Wikipedia? It is in no danger at all. Funding it even more lavishly probably won't help it achieve its goals more effectively; it's dependent (by design, and for good reason) on volunteer effort, which is the real bottleneck.
I feel like my Wikipedia-boosting bona fides are pretty solid on HN. I think it's not just a very valuable resource but also one of the great intellectual achievements of the last 100 years. My point isn't that the project is unworthy; it's that they don't need your money.
If you want to help Wikipedia, the best thing you can do is contribute to articles. Time and expertise is always going to be a more valuable donation than anything monentary.