If you are an environmental reporter, it is only a matter of time before a reader asks you, "What's up with pentachlorophenol?" Or a grouchy editor demands to know, "What's the difference between trichloroethylene and trichloroethane?"
Help is on the way.
You can find lists of many of the baddest chemicals in U.S. EPA's Consolidated List of Lists, which gives info on what laws regulate them.
For some of these, the federally required Material Safety Data Sheet (MSDS) gives basic safety and toxicity information. You can usually find them by Googling the name of the chemical followed by "MSDS." Nowadays, searching for the chemical name in Wikipedia can provide good information, too.
For deeper background on the health effects of a wide range of chemicals, a great starting point is the National Library of Medicine's collection of databases, TOXNET.
For all data sources, it is good to cross-check against other sources.