Encyclopaedia Metallum, The Metal Archives
With the nature of the Internet being what it is, a site like The Metal Archives has been around for a long long TIME - since 2002. It is a resource for metal music, the likes of which, I don't believe has been created for any other form of music. Right now, there are over 100,000 metal bands listed in its searchable database. There are over 25,000 independent record labels listed as well.
We consider The Metal Archives to be the authoritative list, the Wikipedia if you will, of the bands and their subgenres within Metal. In fact, I think posting this article has probably goosed the staff here to start putting up an additional "Resources" page here on Thermionic that will tell you about some of the places we go to look for material for posting.
Now all that being said, for all the information in the pages of The Metal Archives, a quick search of a well-known band like, Orchid results in a a few pages that will reveal huge amounts of information about bands with Orchid in the name, (including a Metal Archives page for Orchid) but no link to the website of the band that we're actually looking for. The page describing Orchid, it's location, it's members, its albums, and reviews of those albums has no link to Orchid's homepage. Neither does the general alphabetical listing of bands in its pages.
Despite the huge number of bands in its pages, the extensive list of bands in its pages is also not exhaustive. It might not even possible, despite huge numbers of updates (today already has almost 10,000 entries or updates!) to make it exhaustive. Bands form and break up all the time. The effort of keeping up is herculean: Some bands that are showing promise can't currently be found in its pages. For example, White Light Cemetary.
All this said, we can't think of a better place to go to get access to bands, the genre you want, and a huge wealth of material far above and beyond what you could get anywhere else - including album reviews, links to CDs, vinyl, and band merchandise - and other assorted pieces available through merchants like eBay.