Opening geodes is always a lot of fun. You never know what is inside until it is open, therefore, in order to get the most enjoyment out of your geodes, you have to crack them open. There are a few ways to do that:
 Professional geode crackers use a set of two hardened steel points fastened to a power press, which allows you to apply pressure on the geode from two points at the same time. This is a great way to open a geode, but it is a little bit expensive.
 The method I prefer to use is a plumber's pipe-cutting tool. These can be found for sale on the internet and through plumbing supply houses. To open a geode using this method: find the most logical fissure or wrinkle along the outside of the geode; lock the geode in the plumber's tool and apply slow, even pressure to the handle. The geode will almost always open with a nice, even crack (no jaggies).
 One method is to score the geode all the way around rather deeply with a trim saw. Do this by raising the splashguard and rotating the geode by hand until it is cut all the way around. Now you can use a screwdriver to pry the two sections of the geode apart.
 The most common method is to lay the geode in a soft (earth) depression. Look the geode over for any cracks, weak spots, or lines that look like they might be good places to crack it open. That' where you need to apply pressure. When you have found the ideal spot on the geode, use a medium weight hammer (or rubber mallet) and center punch (NOT A STEEL CHISEL). Put the punch in a spot most likely to keep if from sliding off, and hit it several times; easy at first, then harder. If three or four blows do not open the geode, repeat in other spots until a crack does appear. Then use a screwdriver to pry your geode apart.
No matter what method you use, always use gloves and safety glasses. After you have cracked your geode, put the halves back together and secure them together with tape or rubber bands until you get them home. Never hit geodes with a hammer! Although you have on safety glasses, chips from the geode will fly in all directions, placing everyone around you in danger, and leaving chips of the brokern geode strewn all over the ground. Don't open the geodes in the field . . . take them home or to your shop or to someone who can open them for you . . . and leave the property from which you collected the geodes in just as good or better condition than it was when you arrived.
If you have additional information about geodes, unique or interesting ways to open them, or information on geode collecting sites, please leave a comment to this post.