I have used a rock picker that you pull behind a tractor. It will pick up most surface rocks. If you are just going to clean up a field for plowing or planting you would be better off to rent one if you have a big enough tractor to pull it. Rock pickers are heavy and it takes about 70 HP to move the one we used.
The bucket that TRnCO posted might work pretty well on some fields and there are other brands that have longer front times which gives you a deeper bin to hold them in. Have not used one so no comment on that.
