Caltech Theoretical Particle Physics - Research in superstring theory, quantum gravity, quantum field theory, cosmology, and particle phenomenology. - http://www.theory.caltech.edu/
Shri Kulkarni's Group - Research extra-solar planets, compact objects and pulsars. Recent preprints available. - http://astro.caltech.edu/~srk/
The InfraRed Army - InfraRed Astrophysics - http://www.cco.caltech.edu/~btsoifer/ira.html
FemtoLand Group - Femtosecond spectroscopy and dynamics - http://www.its.caltech.edu/~femto/
Caltech Observational Cosmology - Observing cosmic background radiation and other phenomena at infrared and millimeter wavelengths - http://phobos.caltech.edu/~lgg/