I've found some interesting old things around my place - I live on a very old (by California standards) property that's been inhabited forever. The indians were here before the settlers started building things in the 1800's. Since a creek runs through the middle of the property, and every time the creek floods it adds a few inches of sediment, there are all kinds of old buried artifacts that I keep finding. Mostly old bottles, plates, pottery, tools, etc. I did find an old brick foundation to a very old building while digging a trench for electrical service. Also found a big 'cache' of really nice red and green Jasper boulders - someone had apparently collected it from a deposit and was storing it for future use.
Oh yeah, I found a 100+ year old hand-dug well (6' x 6' x 50' deep) by accident one day. I was tractoring around, and the tractor just dropped when it went throught the old rotten wood lid to the well. Aside from the scary factor, that was a really cool find. The well is still in perfect shape, and I can't imagine what it would cost to build something like that today. I reinforced the top of it, poured a slab with an access door, and then built a shed on top of it. That well produces huge amounts of water even in drought years.