Blackberry.
It will take several years from this stage to produce fruit, so it depends on whether you just want to let it set its natural course, or if your looking for more immediate results.

It's a Blackberry. I dug a couple small ones up last year, from my Father in laws and this year they have berries.

Thanks guys - there are a few just over the fence in the neighbor's yard that hadn't been mowed, and they have berries on them. They are shorter than I thought blackberries would be, and are covered with small bright red and shiny black bugs. They're kind of scary looking - not sure if we want them around if they come with the bushes.