WARNING - addicting ...you will see...BUT, you will find out everything you thought you knew.
http://forums.delphiforums.com/mineralmania/startTheir start page has lists of MMU companies, as well as other types of all natural companies (soaps, herbs, essential oils, skincare, etc)
There are also full blown forums for Bare Minerals (Escentuals), Philosophy, MAC, Make it Yourself, Garden of Wisdom, Be Beautiful Cafe....endless. That said, I would start with Mineral Makeup Mania. There are also some non Delphi places as well to get an overview of mineral makeup.
http://www.themineralmakeup.com/http://www.makeup.com/forum/forums/show/6.pagehttp://www.makeuptalk.com/forums/f128/http://makeuptalk.wordpress.com/that said, I have used nothing BUT MMU for years...and not that crap with the bismuth in it from Bare Minerals and Sheer Cover...there are a lot of private, home based companies that are passionate, fabulous and follow FDA rules AND have better product for better pricing. I believe even Merle Norman is doing a REAL pure mineral makeup
You have to be careful what you are getting. The crap at the drugstore is NOT pure mineral..there are tons of parabens in these things as well as ingredients that are not mineral...label reading is your friend.
I am currently using stuff from Bare Faced Minerals
http://www.barefacedminerals.com/Meow Cosmetics
http://www.meowcosmetics.com/and U Glo Girl
http://www.uglogirl.com/however, I will sample purchase when I am bored from many others.
Most home business makers have samples so you can buy a little to get a color match. Many places will absolutely work with you on a color match through photos or, if you have a sample of makeup you must, then have custom blending. Bare Faced Minerals make one with Vitamin E for...ahem...mature skin...there are so many blends, some with more mica, some with more zinc oxide...
One thing I have discovered, if you are going to use mineral makeup, your skincare regime has to be...sheesh...regular and meticulous. Since buffing is involved, you will learn more than you ever thought about brushes (synthetic and natural bristles) and sponges.
You will either love it and become addicted, or hate it...I do not think there is real middle ground. If you are a no chem/no syn person, it is a must. Plus, many are totally cruelty free and vegan as well. I would never go back to off the shelf makeup again.
Whew, fairly opinionated too! Sorry....no offense aimed at anyone who chooses and love BE, JI and Sheer Cover either