MyRockSite.com is one example of a resource for an alphabetical list of rock bands. Wikipedia features an alphabetical list of metal bands and alternative rock bands.
My Rock Site also features information on rock bands such as discographies, names of members, short biographies and links to fan websites. Examples of rock bands in this database include Alice in Chains, Bullet For My Valentine, Def Leppard and Fall Out Boy.
Bands featured on Wikipedia's list of heavy metal bands include Quiet Riot, Twisted Sister, Metallica and Iron Maiden. This list focuses on heavy metal bands from the beginning of the metal movement which took place from 1967 to 1981.