I only recently started drawing again after a long hiatus, and I find myself using references a lot to get the details of my art right - building shapes, perspective, anatomy, and so on. Reference photos are an immeasurable help for a newbie like me, since they make me aware of details and subtleties which I ordinarily wouldn't even think of when drawing something.
And I am sure that I am not the only one who uses them. Thus, I propose that we use this thread to share links to the various online photo galleries that we use for references so that others can use them as well.
Here are two I have used:
Science and Society Picture Library: This is the one I tend to use the most, since it has a vast amount of searchable images of the Victorian Age on almost any conceivable topic - perfect for my own comic.
OKCupid Quickmatch: Basically a "random member" function of a popular online dating site. It calls up random profiles of members.
Of course, we don't care about actually dating all these people (or do we?

). But you get a vast amount of pictures with which you can practice drawing profiles and faces! After I bought my graphics tablet, I used this for my first exercises - I drew lots of these faces, and never spent more than 10 minutes on each of them (the point of this exercise was not to draw them
well - hard to do for a newbie - but to get the basic shapes and forms right in a quick and efficient manner...).
Any others?