With hollowpoints they explode quite dramatically. FMJ rounds .. still explode quite nicely with 9mm, .40, and .45.
Silly string from the dollar store is also good. For a REAL blast get yourself an exploding target and tape it to a can of dollar store air freshener
I spend about $1 per target for good targets at the sporting goods store or even wal mart. At the dollar store ... EVERYTHING is a buck ... and its ALL fun to shoot at.
We have grabbed everything you can imagine from there and never had a bad time shooting at any of it.
Oh .. the 16oz soda cans are 4 for a buck and if you shake them up real good before putting them downrange they can be fun too!
**added**
I forgot a couple things ..
For the shotgunners out there .. if you can get a good toss on a can of shaving cream ... priceless .. we use a water balloon launcher to throw things up but small modifications to a throwing machine will work with cardboard and duct tape.
I consider myself lucky to have a place in northern MN that is on State owned land where we are able to have this much fun. Never had a complaint but then again the last 3 times we have been there we left with as many 55 gallon bags of trash (mostly from other shooters) as we could carry.