A friend of mine and her husband dug this up while trying to do some planting (in Kansas). They’ve never seen anything like it. I can’t find anything that really looks like it online, either, plus I’m not even an amateur entomologist. I just tweeted it to @phil_torres, but I know we have some super spidey people here, too.
There are 5 pictures at the link. The last one shows the spider sitting on the blade of a post-hole digging shovel, which should (I hope) give some idea of its size.