Hey Deadna, I'm sorry I didn't get back to you about mold materials. Things have been hectic lately!
I would have PM'd this, but you have PMs disabled, so...
The biggest concern when choosing mold material is what will you want the final castings to be made of. Some materials are incompatable, or just too much of a hassle to use together. This ties in with the physical aspects of both the original and the casts. Undercuts and such will influence your choice of material and type of mold. Another consideration is the run size. Just how many castings do you want, versus how much money, time and effort you are willing to spend.
For overall versatility, silicone works well, but it is useless for casting latex. Good for polyurethane foam, plaster, cement, resins, and many casting materials.
Urethane makes for a durable mold, but not as flexible as silicone and again, not for latex.
Latex works well for casting cement and the like.
There are many materials you can use to make a mold.
You'll need to use the appropriate release agent, again, that depends on the materials you use.
Here are some companies that carry molding and casting supplies.
http://environmolds.com/
http://www.polytek.com/
http://www.reynoldsam.com/
http://www.culinart.net/index.html
http://www.smooth-on.com/
http://www.industrialpolymers.com/wa...urethanes.html
http://www.shopmaninc.com/index.html
http://www.accu-cast.us/
If you have any questions please feel free to ask me.
Good luck!
Lurks