There is a ton of info on making your own mix at the Container forum.

Here is an organic blend I make myself:

For Blooming Plants:
2 part peat moss or coconut coir
1 part vermiculite
1 part pumice or perlite
1 part compost
2 tbls bonemeal or softrock phosphate per gallon of soil

This works great for me, but you do have to water it frequently. Also, if you're going to have the same plants in the pot for years, organic blends can get too compact/dense (or so they say on the Container Forum). So this works best for seasonal pots.