You are lucky! Most of the rock around here is flat or layered, which is beautiful, but round stones are also very nice. I found some, but there aren't as many where I live. Some ideas for using the rocks:
1) lined garden beds
2) stone birdbaths
3) walls or pillars
4) a round berm/rock garden with round rocks lining the perimeter
5) decorative "cobblestone" pathway with rocks imbedded into cement
6) dry creek bed ( If you don't like a flat creek bed, then you can berm up the ground near a corner of your lot--have 5 yards of topsoil dumped there) which will create a nice slope for you to create your bed.
7) pond bottom

Try posting your message in the "you folks with rocks galore..." thread in this forum. There seems to be many folks wishing they had your problem. Some have even claimed they'd travel to get rocks. Perhaps you can call their bluff...? Then again, they might show up at your door.

i know this is a bit late for a response. But there are
houses in the north east/ esp new york state that are
built out of the cobbles you have. some are very interesting. maybe you could buils a small shed. Its a very
specific type of masonary work and i don't know where i read about it-- but it was in the last 2 or 3 years-- could have been national geographic article. But just an idea.

You truely don't know what you have. I have spent the last 5 years doing dry stack walls with the same stuff. It is incredable. Start with the smallest 1st. then gradually go up in size, with the top stone covering the the lower two. work in really small ones in the gaps to help block some holes that soil can exscape from. I have terraced my 3/4 acre lot with these, and had to go find a few more to finish the projects. I also have 24" high round free standing bed for flowers (8 ft diameter). You can free form any size and shape beds you want. I also inter mix really large stones periodically to change the dynamics of the the bed, and then peice together the smaller stones around and up over the larger rock. once you figure it out, you will be hooked. Have some fun.

Here's what diggerb2 was talking about. The actual cobblestone buildings are amazingly beautiful. Unfortunately, there aren't too many images on the web. If you'd like some more examples, I could take my digital camera out for a drive :)

Here is a link that might be useful: example of cobblestone construction

I saw a nice wall made of "gabions" - wire mesh forms filled with round dumpy river rocks.

So you are the Dwight Frye of rocks eh
Look into slip form construction- Helen and Scott Nearing were big users of that method.
Gabions are amazing structures, originated in China using bamboo baskets, now heavily galvanized wire.