The most basic choice, the problem with the wizards is that they’re often slightly lacking in necrotic hitting power and thematic powers (favoring fire and lightning and other not-quite-Underworld-seeming special effects). But their spellbook mechanic is very thematic, as is the cantrip use, and the controller aspect suits the necromancer as a whole.
Portraying the necromancer with wizard mechanics mostly a matter of picking spells like ray of frost, ray of enfeeblement and freezing cloud over more flash-bang spells — though there’s also room for reskinning, say, wall of fire into “wall of the pyre” and describing the charred bits of bone and ash dancing within the flames.
Probably the most instinctive of the PHB1 builds for necromancy, the imposition of conditions maps fairly well onto necromancy as a curse delivery model. “Orbs” made in Hollowfaust are likely skulls, covered with a layer of metal (silver, lead or black iron being common), carved with runes, adorned with jewels or a mix of all three.
The staff of defense implement mastery may represent a necromancer who has a guardian spirit bound to him. Staves made in Hollowfaust are likely made of bone, of course: fused vertebrae, or long bones melded to one another.
Potentially rarest of the builds, as it’s the least scholarly by nature. A necromancer focusing on accuracy is likely using a pointing bone of some sort.
The summoner option from Arcane Power is a strong contender for “best potential necromancer build.” This is a good starting point for the Animator’s Society, and to some extent the Speakers. These represent temporary animations, or the conjuration of spirits. The only slight problem is that many of the summoned beasts look at first blush to be… well, not very necromantic in theme. Some recommended reskins follow.
Summon Fire Warrior: Summon Ash Ghost, conjuring the burning spirit of a citizen of Sumara who died in the eruption. Ash ghosts are not strong and are unlikely to slip the summoner’s control, making them a suitable spell for journeymen to master.
Astral Wasp: Bone Imp, one of the most basic creations, little more than a cluster of bones that support a biting skull.
Summon Abyssal Maw: The damage being untyped, this could be a basic skeletal warrior with a weapon of the caster’s choice.
Summon Arrowhawk: Summon Bone Kite, a flying creation that may be a reanimated flying beast such as a large raptor or small drake, or a chimerical invention taken from the bones of many beasts.
And so on.
A recommended option for the Sowers of Fear, who focus on psychic damage. Most of the illusions will be taken from nightmares, born of the necromancer’s mind or from that of his prey. Should be fairly easy to manage.