There is line of sight hardware avaiable, such as radio, microwave, or laser, but each it pretty costly. I have seen some webpages that show how to take an old Satelite dish no longer in use and convert it for use as an 'antenna' for a wireless connection (directional obviously), and if you can build 2, I don't see why you shouldn't be able to connect them to eachother that distance away, and use ICS to share internet.
I THINK there was a thread here about 8 or 9 months ago about it, but the search function doesn't seem to be playing nice with posts older than the recent upgrade we did, so you would have to look through the threads one at a time...