Good Labels:
(old school) 4AD: Cocteau Twins, Bauhaus, Dead Can Dance, This Mortal Coil, Clan of Xymox.
Black Mark: Bathory, Edge of Sanity, Nightingale, Dan Swano, Morgana LeFay. Best adverts ever. A sample:
"Now It's here! Finally released from the chains of Christ, the second offering from the dark merchants of brutal yet symphonic death metal. "Unorthodox" contains 12 tracks of blasphemic hymns to the darkside, ranging from demonic speed to mournful ballads. Get it while you are alive. A definite tombstone in the history of Death Metal
...IT WILL LEAVE A BLACK MARK IN YOUR FLESH!!"
Century Media: Arch Enemy, Behemoth, Bloodbath, Borknagar, Dark Fortress, Dark Tranquillity, Dream Evil, Finntroll, Grave, Napalm Death, Nevermore, Sigh, Strapping Young Lad, Tiamat, Unholy Ghost, Vital Remains, Warmen etc.
Deathlike Silence (RIP): Only made 9 releases, which include 'De Mysteriis Dom Sathanas', 'Deathcrush', 'Scorn Defeat', 'Burzum' and 'Aske'. Despite any other faults he may have had, Euronymus really could pick 'em.
Earache: Blood Red Throne, Carcass, Deicide, Ephel Duath, Ewigkeit, Iron Monkey, Lawnmower Deth, Mistress, Mortiis, Lawnmower Deth, The Berzerker.
The End: Agalloch, Virgin Black, Sculptured, Frantic Bleep, Voivod.
Nuclear Blast: Agathodaimon, Amorphis, Anthrax, Bal-Sagoth, Blind Gaurdian, Candlemass, Cathedral, Death, Grave Digger, Graveworm, HammerFall, Hypocrisy, Immortal, Meshuggah, Nightwish, Omnium Gatherum, Orphanage, Pungent Stench, Secret Sphere, Sonata Arctica, Stormtroopers of Death, Subway to Sally, Therion, Wintersun etc. etc. Very commercial, but they sell fucking Hypocrisy pyjamas. Rock!
Osmose: Absu, Arkhon Infaustus, Black Witchery, Impaled Nazarene, Melechesh, The Rocking Dildos, Swordmaster, Yrkoon etc.
Peaceville: My Dying Bride, Darkthrone, Katatonia, At The Gastes, Opeth, Paradise Lost.
And a load more. There's lots of labels, like Noise records for example, that have had, at various points, loads of great bands, but aren't that good nowadays. Others have one or two good bands but aren't worth mentioning otherwise. Quite a few of my favourite artists, especially the neo-folk and black metal crowd, self-release or run their own small labels/distros with a few side projects or smaller bands on the side.
I'll also back Storm Rider up on Inside Out. Quality label, and also, if we're allowed distros, then Seven Kingdoms and the sadly defunct World Serpent are clearly the greatest ever.