Selling Your Digital Photos - How To: MSN Tech & Gadgets:

Even if you're not planning on going pro as a photographer, having a bit of money come in now and then can be quite nice (as well as being remarkably handy when it comes time to convince your other half that you really could use a better flash (or lens, or body, or tripod, or set of filters, or camera bag, or larger memory cards, or computer upgrade or whatever)).

Personally, I think the stock market is pretty much flooded these days - that's not to say you can't make a bit out of it, but I wouldn't expect it to offer any more than occasional coffee money. Personally, I'm steering more towards the 'Old Fashioned Way', as mentioned in the linked article - take a bunch of great shots, get them framed/mounted/whatever, and sell them at local fairs. I'm shifting town in a few months, to somewhere a lot more tourist oriented - and I really expect that to take off then...