Some useful stuff:

• Molecular Astronomy Resources:
  
• Line frequencies and energies above ground state can be found on the JPL Spectroscopy Group homepage. Information on the format can be found here . (Look up page 13 on how to calculate A-Values). Dipole moments are also listed in this document or in the the .pdf files listed here. For frequency listings start here.
• Lines not in the JPL catalog and extended and critically reviewed entries from the latter can be found in the The Cologne Database for Molecular Spectroscopy.
• Lists of (far)infrared atomic, ionic, and molecular lines can be found on this page at the MPI für extraterrestrische Physik (yes, I have made copies of these, just to be on the safe side).
• An incedible wealth of molecular (and other) data can be found on the NIST Physical Reference Data site as well on the
• NIST Chemistry Webbook site. Start by clicking Species List in the Documentation listing to get a zip'd ASCII file (yes, it's that big!) from which you get the code for the species you're interested in that must be used in further searches.
• The DiRef database is an ongoing effort to make online and update the contents of the classic Huber and Herzberg book "Constants of Diatomic Molecules." You have to register and they send you a password. The scope of the effort is described here. 
  

• An extremely useful collection of astrophysics data and formulae is Martin Zombeck's Handbook of Space Astronomy and Astrophysics.
• Latest values of the Fundamental constants can be found here.
• A recent report on working at high altitude is here.