I think tabfinder has a nice diggin tool above. Personally, I use a large Pakistani knife I got at an auction for $7 fifteen years ago. It is dull now, but is practically indestructable. I have levered huge rocks out of holes with it. I keep a sharp knife in my pocket or on my belt for slicing through roots when necessary. Diggin' tools used can be as creative as you can get. I would like to offer some suggestions though, but keep in mind that the best tool is one that works for you. For yards/parks/public areas you want something that is small and portable and non-threatining looking. Sharpened Flat trowels are good, but I like knives better. They make a nice clean hole every time. I also hinge my plugs so that the grass has at least a fighting chance of growing back. I dig the plugs deep (less messing with grass roots and also more likelihood that the target is in the plug and out of the hole). I sometimes get a little self-conscious about bringing a 16 inch long knife into a park, but I purchased an ugly green plastic small bath mat from the dollar store about the same time I bought the knife. I use this to kneel on as well as place the dirt on from the hole. It is indestructable as well, and I can blast it with the garden hose and fold it into quarters to pack it with me. This ugly little mat serves many functions. First, the target has no chance of escaping down into the grass again when the extra dirt is placed on the mat. Second, it is a little softer on the knees and I get no grass stain on my pants now! Third, there is less mess when I fill the hole in since the dirt is not spread all around. In most cases you would have to really hunt for my plugs to find them! And last but not least (and also the reason I mentioned the bathmat in the first place), I can wrap it around the knife to hide the knife from view. Never had any problems with it. I hope this helps.
Buckleboy