As I shoot mostly out in the country amongst some rolling hills, I shoot lots of different things. One of the best so far has been a brand new propane tank, empty of course!! It has been out with me 4 times and taken untold rounds of .22 as well as a bunch of 7.62x39. I can also get scraps of spring steel from a nearby shop. I drill two small holes to hang them from, quick paint job, and hang them from a 2x4 target tree with some black wire. You always know when you hit them and cheap like borcht!!
Cheers!!