The primary web tool: www.google.com
Most preprints now appear in the Los Alamos e-Print archive at xxx.lanl.gov (or its UK mirror at uk.arxiv.org). The preprints have labels like
hep-ex/0210049
where hep-ex means "High Energy Physics - experiment", the 02 is the year, and the rest is an identifying number. There are other categories like hep-ph (HEP phenomenology) and hep-th (HEP theory), astro-ph, etc. If you have a reference to a paper (such as the one above) and you want to look at it, go directly to
xxx.lanl.gov/abs/hep-ex/0210049
This will take you to the page with the abstract and links to the full text document. If you don't know the number, then there are search facilities provided from the main archive page xxx.lanl.gov.
Found at www.slac.stanford.edu/spires/. Particularly useful is the HEP literature database, www.slac.stanford.edu/spires/hep/, with information on a half a million HEP related papers. For some (most?) links to the full-text document is given. For others you only get the reference to journal publication.
SPIRES also provides links for conferences, experiments, HEP institutions, journals, etc.
Located at pdg.lbl.gov, this site contains downloadable versions of the Review of Particle Physics, which is the main collection point for HEP results. There are also links to other databases with, e.g., tables of cross sections.
For Rhysical Review and other APS journals, go to publish.aps.org. Similarly, google for "the journal you want" "online", etc. Abstracts are free, full-text document is usually only available with subscription. CERN subscribes to almost every HEP journal you'd want, so if you run your browser from a CERN account you can get access that way.
The library page is at www.rhul.ac.uk/Information-Services/Library. The main catalogue is online, as well as links to other catalogues.
By following the "Resources" link you can access a number of online journals (although not many related to HEP except Physical Review Letters). From non-RHUL computers, this requires an ATHENS password, which you can get from the library.
Located at library.cern.ch, this site contains among other things links to all of the online journals to which CERN subscribes.
Found at www.desy.de/html/infodienste/bibliothek.html. Contains the usual stuff (like CERN).
See www.hep.net. Similar to the corresponding CERN and DESY sites. Contains a spooky 1995 link to the SSC.
All major Particle Physics collaborations maintain their own websites, which contain handy links to their documents, publications, etc. Lists of experiments can be found, e.g., through SPIRES list of experiments.
Essentially all particle physics conferences maintain a website with links to submitted papers and often to conference proceedings. For example, check out ICHEP02 or Moriond 2002.
Various sites, e.g. SPIRES, maintain lists of conferences.
Found at physicsworld.com, this site contains a reasonably interesting online journal and a list of job offerings.