Molecules App for iOS
'Molecules is an application for viewing three-dimensional renderings of molecules and manipulating them using your fingers. You can rotate the molecules by moving your finger across the display, zoom in or out by using two-finger pinch gestures, or pan the molecule by moving two fingers across the screen at once. These structures can be viewed in both ball-and-stick and spacefilling visualization modes.
New molecules can be downloaded from either the RCSB Protein Data Bank (http://www.rcsb.org/pdb), an international repository of biological molecules and their 3-D structures, or NCBI's PubChem (http://pubchem.ncbi.nlm.nih.gov), a public database of compounds. Molecules can be downloaded directly to your handheld device and stored there for later viewing.'
This is a free app.