Well for most Necromancer centered builds it's best to stick with a spellcaster weapon (wand/offhand or a staff). That said, I usually do have either a longbow or a flatbow with me at all times for pulling mobs of creatures.
To get technical there are some weapon "modifiers" that are particularly useful that you should be on watch for. Generally necromancer weapons with "Half Casting Time" or "Half Skill Recharge of Spells" mods are very useful and sought after (this is true of almost every spellcasting proffession as well).
Also a weapon with a +1 Death magic on skill activation are also useful for Minion Masters.
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