Spent some of my afternoon snapping photos of some local historical sites that needed documentation. Start here, my area is packed with stuff but I clicked around some less populated states & counties and pretty much every county has at least one thing to take pictures of.
It was a fun excuse to get outside, the contest runs until the end of September I believe. I did this partly to help clear my conscience of all the times I've used Wikipedia.
It looks like this is US only, I couldn't find anything for international monuments, sorry. International site courtesy of fiveop: http://www.wikilovesmonuments.org/