Scholomance Key (Alliance & Horde)
Travel to Tirisfal Glade and go to the Bulwark in the west edge just before Western Plaguelands and talk to High Executor Derrington. Get the quest All Along the Watchtowers, it's marked as elite but it's very easy to do solo as the elites inside the towers won't aggro. Mark all four towers and return to High Executor Derrington and turn in the quest.
Now you get the quest, Scholomance. Talk to Apothecary Dithers and get the next quest, Skeletal Fragments.
Go back to Andorhal and kill the skeletons inside, you need 15 Skeletal Fragments to complete it. Get the fragments and turn in the quest and get the next one, Mold Rhymes With...
Make sure you have 15 gold and then travel to Gadgetzan in Tanaris. Talk to Krinkle Goodsteel and get the next quest, Fire Plume Forged.
Get two thoium bars from the Auction House if your not an miner or ask someone for them. Travel to Fire Plume Ridge in Un'Goro Crater. Go to the lava lake at the mountain and rightclick the Skeleton Key Mold there. Go back to the Bulwark and turn in the quest at Apothecary Dithers and get the last quest in the chain, Araj's Scarab.
Get some more people to help and go to Andorhal and kill Araj the Summoner, return to Apothecary Dithers to get your key to Scholomance.
Gratz, now you'll never have to be in a group without the key!
The Alliance one (As I read about it) Is exactly the same except guys are at another spot, Chillwind Point.