Carl Griffith's 1847 Oregon Trail Sourdough Starter is great stuff! I've been using it for about 6 months now and it works flawlessly.

You can get it for the price of postage. Go to the page for the Friends of Carl and get your own. You send them an addressed envelope and a dollar for postage. In a few weeks you get back a plastic bag with a tiny amount of chunky white bits. Follow the startup instructions and you'll have a very robust sourdough starter that makes great bread.

I make one loaf a week. The culture remains dormant in the fridge all week, then on Friday evening I take it out, stir in one cup of flour and one cup of water and leave it loosely covered with wax paper overnight on the counter. The next morning it has bubbled up and is ready to go. I use recipes I've found on the web and in Donna German's bread machine cookbook (I don't use a bread machine but the recipes work fine). The one modification I made to her recipes was eliminating the added yeast. I let the starter do all the work. It takes longer but the taste is much better. The first rise takes about 2-3 hours and the second rise takes about 1.5 hours; 30 minutes of baking later, I've got a delicious loaf.

You can't go wrong with Carl's great starter.