Genetic Code This reference tool provides an entire codon table as well as information on about 20 amino acids. It also includes chemical structures, polarity, charge, pH, etc.
Molecules This app allows you to download and view 3-dimensional molecules that you can manipulate with your finger tips.
Atom in a Box Atom in a Box is great for physics nerds. It's a great aid for visualizing the hydrogenic atom orbitals and the 3D states that the electron occupies in hydrogen (totally taken from the app description!) It allows you to explore all aspects of the atom from your iPhone.
Pocket Universe: Virtual Sky Astronomy Pocket Universe is great for stargazers. It displays constellations with or without the horizon line and it includes directional arrows to help you find them based on the time and your location. It also includes a constellation quiz, viewable objects, sun rise and set times and moon phases.
Epocrates Epocrates provides information on over the counter drugs. It includes active ingredients and interactions. It's also updated once a week.