heard good about these
http://shop.ctstore.com/store/pc/viewPrd.asp?idproduct=17&idcategory=3
https://www.amazon.com/Franklin-Sports-Aero-Strike-Plastic-Baseballs-Pack/dp/B003GCJLC2
Here's another brand of plastic baseballs that can be turned into russian-style juggling balls ($8 for a set of 8): http://www.amazon.com/Franklin-Sports-Aero-Strike-Plastic-Baseballs-Pack/dp/B003GCJLC2