I most often use tennis balls. I agree they aren't ideal, but their chief advantage is safety and the fact they don't go nearly as far as stones or golf balls can actually be a plus as retrieving them is easier. However I just spent a week in the country where I had the chance to throw a few good river stones Seeing a stone go well over 100m for the same effort that would barely get 50m with a tennis ball was very satisfying.

My favorite ammo out of what I have used in the past would definitely have to be river rock.
But alas, due to a cruel twist of fate, I am smack dab in the middle of a city, and am forced to use tennis balls to prevent property damage.

I'm fortunate enough to live in an area that was once under water (South Jersey).  Consequently there are zillions of oval shaped egg sized river stones around here.  They are generally my ammo of choice.  I like golf balls a lot too because they do fly farther than anything else I've tried.  There are lots of golf courses around here so I never have to buy them.

Geo wrote on Jan 22^nd, 2010 at 8:21pm:

To avoid losing them, I've read of some people tying a bit of ribbon to them to make them easier to follow and find.

You answered your own question.

Rocks. Very dense, very smooth. Either spheroids, ovoids or spindles. Lots of all the above around my "ranges" (where I live used to be the bottom of the ocean, then was smashed up into a big mountain range , then was eroded from around 1500m tall down to the 500m mark.Then had some volcanoes make a mess all over the place.

Lots of rocks, and space. Good combination.

But I do like your "stuff" approach, CA... I think a weekly segment called "Can You Sling It?" would be great.

Fruit, veg, lumps of steel, a few lengths of old, fine chain (actually that was fairly impressive), bits of wood, darts, bones, all very fun. I tend to ritually launch the last few inches of any given cucumber (grow our own, can always cut fresh), the occasional rotten egg, not often as being freerange they take forever to go off... there's a half a sack of readymix in the shed I keep meaning to play with to make more glande shaped shots but not gotten around to it yet.

I have never (confession time) actually slung a ball. Tennis or golf. The dog eats them so by the time I see them they're a withered husk of their former selves. Yes, he really does eat golf balls. Every now and then we find some somewhere and within a week they're just shreds of plastic and a hundred metres of rubber.

Tip - don't let a rhodesian x ridgeback chew your balls, if you value them.

rocks ans snails.