I guess everyone's heard of Wikipedia by now, but probably not as many of you have poked around in the Wikimedia Commons, which is almost equally fun in its own way. The Commons is a place for people to contribute Freely licensed media to the world. It's not necessary that Commons pictures have encyclopedic value (although, of course, many do, and are referenced by various Wikipedias); it's merely a repository of images that someone, someday, might conceivably want to use in some kind of publication.
When I get tired of the anarchic process of wrangling with other editors on Wikipedia, I switch my contribution energy to uploading a few of my better photographs to Wikimedia Commons. It's a relief not to be forced to butt heads with some obstinate fellow editor on the Commons to defend a nitpicking detail of something I just did. At worst, my picture will simply be ignored. And if a useful picture gets uploaded, then it can get seen by a lot of people. For example, my own picture of the Ontario Legislative Assembly is currently in the Toronto article's "Government" section. (Curiously, no Toronto Wikipedian has yet uploaded a better picture than my tourist shot.) A lot of people are going to see that picture, if only in passing. It feels good to be useful this way, and the pain-to-reward ratio's much smaller than for textual contributions to the Wikipedia.
Also, one of the coolest aspects in Commons: featured pictures, which are frequently astonishing, and comparable in quality to the photographs in almost any "real" publication. Forget Brittanica; the quality approaches that of National Geographic in some cases.
Equally cool, for photographers, is the featured picture candidates page. Reading the discussions is a great way to learn what makes a good expository photograph. As a whole, the editors have a good eye and extremely high standards for technical, compositional, and affective elements of photography.
On the other hand --- as the nomination discussion on my picture of a Spermophilus lateralis reveals --- sometimes excessive cuteness overrules all that. Technically, it's not a great photograph: at full size you can see noise and blur, it's only 1024x1024 pixels (I cropped it down from a larger picture in order to make it a more effective illustration for its host article), and the (distant) snowfield in the background is completely blown out. But it's cute, so...
(This particular photo recently made featured picture on the English Wikipedia, which is a separate process from getting featured on Commons.)
Anyway, if you take photographs --- and digital cameras being being as ubiquitous as they are, you probably do --- then you should really consider uploading the interesting ones to Wikimedia Commons. You'll have to spend some time reading the uploading guide, but after that it's pretty easy and rewarding. I mean, who knew that anyone in the world would actually be interested in your vacation photos?