WebMD, the homeland security Threat-Level-Red health info service.
Seriously, just use Mayo Clinic if you actually have any health info to look up.
WebMD is so focused on potentially selling you something that everything they list is slanted toward the worst possible thing it could be. Look up headache, they say it could be a brain tumor. Look up stomach ache, could be cancer. Got a hangnail? Leprosy.
Mayo Clinic accepts no ads, and thus has none of that pathetic alarmist propensity. WebMD just wants to scare your money out of you.