Pro-Mix BX is one of the most frequently recommended. But then most all germination/seed starting mixes are "organic" since they only contain peat, vermiculite or perlite, and some lime. It only becomes an issue after germination when the seedlings are transplanted to growing/potting mixes.

Just never use any containing "soil" for either stage as long as they are in containers.

Other frequently recommended brands for starting seeds are Metro Mix 360, Foxfarm, Fafard, Gardener's Supply, Johnny's, etc

This link will take you to a list of many discussions of this question on GardenWeb and check one of the many previous discussions of this question on this forum linked below for more recommendations.

Dave

Here is a link that might be useful: The best seed starting mix discussion