I like to use three power tools and one hand tool for pumpkin carving. You can probably work without any one of them, but I own then and they work really well.
1. The Sawzall. The absolutely simplest way to decapitate the pumpkin is a sawzall. Jab the blade into the pumpkin and pull the trigger. In a matter of seconds you have the top removed. Be sure to tip the blade so that the plug is cone shaped. If you don't, you wont be able to pull it out of the pumpkin. I use a 4 inch general cutting blade. It is the same one you can use to cut through 2 x 4 's with nails embedded in them. It works great on pumpkins.
2. Jig Saw. For detailed cuts, I love the jig saw. I once used a manual pumpkin carving tool and it was exactly like a jig saw blade. I use a detailed cutting blade that is used for soft wood. You will need as long a blade as you can get. If it isn't long enough the chunks of pumpkin won't come out. Be careful with the jig saw. You will need one with variable speeds. It cuts pumpkin so well, you will be using its lowest speed. Using the jig saw is a lot like driving on ice. A little gas and the saw will keep cutting. In fact, it will keep cutting long after you take your finger off of the trigger. The pumpkin flesh gives it very little resistance.
3. Router. For some pumpkins you will want some areas to provide a little glow effect. Instead of cutting out the pumpkin, you can just carve away the skin. For this, I like to use my router. I just recently bought a router and there aren't many uses for one, but it removes the skin of a pumpkin like nobody's business. Using the router is easy. I use a 1/4" straight bit most of the time. If you really wanted to remove a ton of the skin area you might want a bigger bit, but the router cuts very quickly. The only warning for using the router is that unlike routing wood where the sawdust blows away, pumpkin flesh just churns up into a pulpy mess. It can obscure the area you are routing quite quickly.
4. Ice Cream Scoop. Once you decaptitate the pumpkin, you will need to scoop out the seed and other goop. An ice cream scoop works very well for this. I am considering sharping the edge of mine so that it cuts through the crap more quickly. One reason you need to do this is to make sure the thickness of the pumpkin flesh is thin enough that your jig saw will cut all the way through it. Be thorough when removing the fibrous gunk on the backside of the area you are going to carve and it will go very smoothly.
Here are some links to pumpkin carving tools that I like to use. I tried to spend some time to find you guys great deals. I think I did a good job of it.