ADA Amazonia Soil and Caribsea Flourite are the most recommended on planted tank websites. Eco-Complete is recommended often too, but the Iron is rumored to deplete in just two years, plus it is really light weight so it's a pain in the butt to plant plants in. ADA is expensive, Flourite much more reasonable. Flourite is available in Red, Dark, and Black, as well as gravel or sand. My personal choice would be the dark or black gravel.
