If you go to
http://www.parkpennies.com/Disneylandpennypressmachines.htm and click on the WDW in the list of links across the top of the page, then look at the links in the upper left frame, you'll find James Mayfield's unofficial list of WDW elongated coin machines in .pdf format. It has a list of all WDW machines, listed by location and updated fairly regularly. My daughter and I collect these, so I print out the list, mark off what we have, and bring the page(s) covering wherever we'll be that day.
As far as EPCOT, every country has a 3-design machine, plus there are many more in non-pavilion areas such as gift shops, Living Seas, etc. These are fabulous cheap souvenirs if you or your kids like them and the kids can have fun checking maps to find the machines in a treasure hunt. If you dont' want to spend all day doing this (and we sure don't) then pick out which ones you want or just decide how many you want during the day and get what you like when you see it.
Also - try to use pennies minted before 1982. They dont' have zinc in the middle like the newer ones. The zinc can be seen in streaks when you press a new penny and that silver color eventually oxidizes and looks yucky as well as possibly ruining the deisgn down the road. The older pennies can be shined up easily, so dont' worry if they're dull - you can shine before or after pressing if you want. I like the dullness, but some don't. Of course, pressing a new penny is better than not pressing, imho.