Particle Data Group (lots of info about elementary particles---for fun, look at the Review of Lattice QCD, written by yours truly)

PDG Live (a more accessible version of the information on the particle data group site)

"About Quarks" at the Particle Adventure Site, which I recommend surfing

Source for soft, fuzzy quarks and gluons: the Particle Zoo

Interactions.org ---a website with the latest from particle accelerators from around the world

Particlebites---the lates in particle physics written by graduate students and postdocs for undegraduates

INSPIRE---the place to search for articles in particle physics and cosmology.

arXiv---preprint archive in many fields

LHC physics center at CERN---latest physics results. See also ATLAS and CMS sites.

Fermilab home page