ASCII art might have emerged from early computing necessity, but converting an image into fixed-width characters remains pretty impressive. Web site Picascii automates the process, generating ASCII art from any image you like.
Using the site is utterly straightforward: either upload a file of your choice or supply the URL for an image you want to convert, and Picascii will convert it into ASCII art, both as HTML code you can paste into a site and as a stand-alone text file. (You can also choose to have the image generated in colour, though this goes against the decidedly black-and-white origins of ASCII art.)
Picascii is free to use and doesn't require registration.