There are a couple prestige classes out there that work well for a good Necromancer.
Mongoose's Necromancy: Beyond the Grave has a Spectral Loremaster, which is a wizard that's primarily interested in knowledge/lore, but uses necromancy to that end. Instead of spending all his time reading books in libraries, he summons spirits of long-dead sages and gets the information from them directly. I give it a high score for concept, but only average score on execution. A lot of the abilities gained are nothing any other wizard can't get. For example, he gains Speak with Dead and Contact Other Plane as spell-like abilties, but that doesn't really add that much to the class, because he can learn them as spells. He gets some other nice abilities at higher levels, like all skills become class skills and true seeing at will, except I'm not really convinced that they fit the character concept that well (or that they're well balanced, either). And it annoys me that none of the class abilities are labelled as Ex, Sp, or Su, and so you're left on your own to figure that out.
Scarred Lands, Hollowfaust: City of Necromancers has the Speaker of the Dead, which is similar in concept. This is more of a spiritualist/exorcist type. This guy feels a bit like that kid in Sixth Sense: he's creepy because he can see and talk to ghosts. He gains Undead Turning, which is interesting because it opens up (for a Wizard) the ability to take certain divine feats that require the undead turning ability. It's pretty well-balanced, but has some pretty high requirements (8 ranks in 4 specific Knowledge skills, plus 2 feats).
Both books have stuff worth checking out for a White Necromancer (although I don't know if they'll have exactly what you're looking for, Falcon). Between the two, I prefer Hollowfaust, because from what I've read (and I haven't read either of them thoroughly), it's more solid in the mechanics.