1. Stick & Sand
Poking holes in the sand or soil is probably the oldest and most traditional method, probably originally employed in Arabian deserts. A simple branch or stick and a patch of soil offers the easiest and most cost-effective approach for those who frequent the wilderness often. The connection with the earth that this affords makes this one of the more ideal options. For those who prefer something that can be employed at home then a Geomantic Box can be created to store some soil, and a Geomantic Wand (created from a thin wooden dowel) can be used to poke the holes. An example of this, with instructions to make one, can be found on page 281 of Creating Magical Tools (page numbers from the Llewellyn 1999 edition) by the Ciceros.
2. Pen & Paper
Pen and paper is the most common method used nowadays and was also quite popular in the Renaissance. This simply involves randomly forming dots or dashes on a piece of paper, in much the same way as randomly poking holes in the soil would be done. This process could also, through paper, be linked to earth. A con to both of these approaches is that they give the diviner too much control over how many dots can be formed, and thus it's possible to consciously choose the symbols one wants to see as opposed to what is accurate of the situation.
3. Bag of Stones
A suggestion from John Michael Greer is a bag or bowl of small stones or pebbles, a handful of which could be taken and scattered on the ground, and then counted to find the relevant number. This could be employed out in the wild with random stones (or other small objects), or a more permanent method could be practised at home. Indeed, they could potentially be painted in earthy or Malkuthian colours, or even in elemental ones in order to form the four lines of each geomantic figure in a single throw.
4. Double-sided Runes/Coins/Sticks
Another suggestion from Greer is a set of double-sided runes, with a single dot on one side and a double dot on the other. This is a fairly quick method of acquiring the geomantic figures, and could make a good gift for the magically inclined. These could be made from wood or stone (both of these preferable for their earthy link) and then painted in earthy/Malkuthian colours or elemental ones. Other alternatives include coins (heads for one dot, tails for two, for example) or specially-created throwing sticks, like the ones you can find here (linked by Scott+).
A final suggestion, recommended to me by a friend recently, is the simple use of dice. An odd number equals one dot, an even number two dots. While many dice you can buy nowadays are plastic there are some that are wooden, which would be more ideal. Indeed, I've seen coloured wooden dice, which could be excellent for an elemental set in order to procur a full geomantic figure in one throw.
Do you have any other methods you employ? Why not share them in a comment?