well I do more than just megalithic stuff.
I used to use a couple of stock librarys in London but most have now folded.
Image Bank is still running but they want to see 20,000 of your best slides before they take you on.
Having an agent is good becasue they often get sales that you usualy wouldn't.
They take 50% but are worth it.
I once sold a slide of a single white fluffy cloud in a blue sky for £8,000.
The internet now makes people think everything is free. Its not, its still copyrighted wether you put up
a copyright notice or not.
I alway crop my photos so that if anyone claims to be the owner then I have a part of the original photo that they don't.