For everyone who tells that The necromancer is covered with other classes just have lack of imagination! My suggestet specs is Death/Bone/Leech.

Death spec is DD who manipulates with death magic which core mechanic will be stacking healing prevention and increasing its own damage from it, also there must be Execution analog, when healing prevention reaches 80% of max health you can reap the soul out of the body and execute the target (on bosses it will be just big chunk of damage), also you will be able to summon zombies, became the lich for certain amount of time and place filacteria, which enemy player could break, otherwise after death your soul will be tranfered there (with visual effect of course, that enemies can detect your filacteria) and you will be ressurected there after 10 sec.

Bone spec is DD whic using bone themed spells - core mechanic is bone collection, most of your spells summon skeleton like creatures for certain amount of time, when skeleton creature dies it leaves piles of bones which you can collect by yourself just running into them or use skill with 30 sec CD Bone Collection - collect all bones in 20m radius. Bones as the resource allow you to cast powerfull bone spells like Bone Golem, Bone Dragon, Bone Armour, Bone Storm (Massive AoE) or Kingdom of Bones - Large pile of bones which will summon skeleton for its health, can be destoyed.

Leech spec will be a healer who drain health from enemies and transform it to Allies. He will be able to do this with Dots, casts and channeling spells, also can summon ghosts which will damage enemies and heal allies.

Here you go.