I always liked shooting Necco wafers. Heck, I'm not even sure they're sold anymore!
I cut the bottom off a CO2 cartridge and ran a 12" length of bailing wire up thru it with a knot on the end. I tied the wire to a tree branch 35ft from my computer desk window. Makes a nice ting when I hit it with my 2289g or my CCS 2400kt 22 carbine. My 22 Disco puts dents on it.
Spent shotgun shells and rifle brass....great to see them fly off when hit.
Got a 1"x 2" with the sharp end of several small nails sticking thru then stick wine bottle corks onto the nails. Got to be zeroed good to hit'em at 25 yards.