Ceramic tile that has a mat finish that has a dark color is a good example. Not only does it collect the sun's radiant heat it stores it as well. Which brings us to the next key point, thermal mass. The same applies to passive solar technology. There needs to be some place to store heat and slowly give it back.
Thermal mass is a major attribute to any energy efficient home - it stores heat.
A good example in nature of thermal mass is the earth itself. The earth's surface takes a much longer time to cool off than the air temperature. That's why the average temperature in autumn in the northern hemisphere is warmer than the spring in the northern hemisphere. Anything that is stone or ceramic is good. Wood has some thermal mass, but not much.