The Metal Archives is one of the best resources on finding information on metal bands (as defined by the site here). To put it easily lets say you want to find some info on Entombed.
You can go to MA, type Entombed into the band search. The band's profile will come up with stuff like the date they were formed, whether they are active or not, all the band's physical releases, who played on those releases and so on. What is also nice is that the site allows you to write reviews for albums so you can get opinions.
The only down side I can find is that the crowd over on the forums is generally a bit elitist but o well, such is life.