Limestone screenings or crushings would be perfect. Either that, just attack it with something, likely a shove and shave off all of the high spots and toss them on the pile you have. It sucks, but it may be worth it in the end, and remind yourself that it doesn't last forever. I suppose that a compactor would work, don't use a jumping jack type compactor if the soil is moist clay though, it will just dig in even more. Rollers on wet clay tend to just turn things into a waterbed, and if you vibrate with it you are sunk. Personally, if I had access to one, I would go with a gas compactor, second option, the shovel.

Good luck.