NYU.edu: Scientific Notation
Curious about the 0.000,000,000,753 kg. mass of a dust particle? Practice notation with sample problems.
www.nyu.edu/pages/mathmol/textbook/scinot.html
UMD.edu: Scientific Notation
Offers a program to practice converting between scientific notation and normal numbers.
janus.astro.umd.edu/astro/scinote.html