When the compost is still kind of rough I have good luck with a tater fork. Then a shovel when it gets broken down.

When I was young and strong I used a big old manure fork.I am a little smater now.

I have an excellent tool for this. It's not a spade fork or a regular pitch fork. The handle is shorter and has a hand-grip at the end. And the tines are sturdier than a regular pitch fork, but not as fat as a spade fork's tines. I get good strength for stabbing a stubborn pile of rotting vegetation, and little resistance at the same time. Something like this:
http://www.amazon.com/AMES-TRUE-TEMPER-Compost-Fork/dp/B000A11EHC
Google for "compost fork"
The hand-grip is very useful for leveraging heavy scoops of wet compost.

thanks

What to use depends on the state of digestion. Early in the process I have used a Hay fork or a 5 tined fork, but a bit later I need the broad forks of the spading fork, and toward the end the material is too fine for anything but a shovel.

Jeremy, while we most use a tool to make work less strenuous, and a fork does a good job of turning most what is involved in working with soil, don't be afraid to bend down and use your hands.
In this way you can feel what kind of action is going on and any heat that is built up with how you are making the pile do what you hope it will do.

Got an old spade handle? Use it to make holes in the pile so that you can sprinkle clippings and get the kitchen scraps down deep before covering.
The wood handle is pushed down, and around and around and no strain is placed on the back.

Once it gets to the finished state, the fork is not the most reliable tool; a spade is called on to transfer it.

The answer to this question DOES depend on the stuff being composted and it's state, AND the type of containers, and your back, BUT ALSO what your comfort level is with spearing lizards! I would feel horrible if I impaled any of the gorgeous alligator lizards who've resided in our pile at any time and it would be just my luck to do so. Furthermore I finally have a generous crop of fig beetle larvae and some sort of huge tarantula-hawk mimic maggot with an uncompostable exoskeleton to protect. Finally the stuff I've got (rotting coconut fiber mat, bromeliads, tangled pads of weeds) is best torn by hand, so I put on the 8mil nitrile gloves and a HEPA mask and move and tear it by hand. And this pile is really beginning to show exciting results!

It's been years since I've posted anything about this, but here goes.....
my FAVORITE way to turn a pile is not to turn it at all!
HUH?!
I like pallet bins.
I fluff em, that's all the turning they really need because the whole point in turning a pile is to introduce air into the pile, (O.k. mixing it is a lil part of turning and busting up big chunks is also a small part)
I have found that if you fluff it starting at the top and working your way down, you can "turn" a pile in minutes and you can do it more often than turning cuz (A) it's a lot easier and (2) it's not as hard to do.
Fluffing adds just enough air to keep a pile cooking and it also encourages worms to breed, the mild disruption of the pile doesn't drive the worms out and in the winter the lil puffs of cold air makes the worms do "it" more, in fact, you can have a compost bin and a worm bin at the same time.
about 15 years ago I made a compost bin and filled it with only coffee grounds that I brought home from Nordstroms espresso bar and in the spring I thought I'd fluff it one last time, so I did, then I went in the house and had a sandwich (peanut butter I think) and when I came back out I thought "screw it, I am going to open the bin and spread my compost NOW". (at that time I only had one bin and I built it on the spot where I was going to have that years garden) so when I opened it up and started to spread it, there was a mass of worms in the center as big as a medicine ball, I have learned since that this was a defensive/protective behavior of the worms, but it was still cool to see.
I have also read that big time worm breeders use ice water to get the worms populations to "bloom".
Pallet bins are ugly, but I have yet to see a bin that is beautiful AND productive

IALBTC (it all leads back to compost)

I found a bulb auger similar to the link below that I connect to my drill and mix.I found that this works really well. I have two different containers. 1 is a home made box and the other is a 55 gallon drum. This tool helps me turn things with out getting to crazy and hurting my self. But if you have an open pile or a light bin then a fork would be fine for turning then a shovel as it get's more fine.

Here is a link that might be useful: garden auger

I use pallet bins. I use a pitch fork most of the time. The fall is when I do most of my composting work. I get at least two piles, maybe three, cooking at 140+ degree F. After the second turn I leave it for the winter. My piles stay covered in old leaf bags to prevent them from drying out. Fresh grass clippings will get very hot and dry themselves in two days. Covered, they ferment and stay composting.

Leaf season is here at last.

Thanks for all the replies. I really appreciate the suggestions and tips.

I picked up a 3"x24" bulb planter/auger from a local store. It works great at aerating the pile and mixing it up. I also bought a compost fork so I can get the stuff on the outside edges into the center. I really like the auger though for daily mixing. I get home form work take off the bin's lid and run the auger into the compost at high speed half a dozen times. It's really easy and takes about 5 min for 2 bins. I need a thermometer; because I swear after I started doing this the pile got a good bit hotter. It's also convenient for burying weeds and animal products in the center. I put about pound worth of zoysia rhizomes that were invading a small flowerbed in there the other day. It really make it easy to put that nasty stuff where it's really hot.

My compost fork works best for me. I found a hardware store that had good selection of shovels and forks (located 1 mile from Home Depot). It has five or six tines, round a curved a bit. The tines are about a 1.5 or 1.75 inches apart I think. this is not a manure fork which is wider.

Don't be in a hurry to buy and read some garden catalogues.

Mine costs thirty or forty bucks I think. A good one cost a hundred or home (stainless and maybe imported from Britian or Germany).