Does anyone know of an item in d&d 3.5 that would allow a character to create spawn similar to the effect of being slain by a wight? I am working on a campaign and looking for an item that creates undead spawn.
Anyone that dies from negative levels will rise as an undead, usually a wight. (citation) So you're looking for an item that inflicts negative levels.
The most naive solution might be a wand of enervate which would cost 21000gp.
A more creative solution might be an unholy weapon, which gives a negative level to any Good-aligned creature that attempts to wield it. This could convert a lot of first-level good-aligned commoners into wights, assuming you also have some sort of mind-control effect to force them to wield it. (Simply handing them the weapon, or placing the weapon on their unconscious body, would not work, so far as I can tell.) An unholy sword would cost 18300gp and change, but I think it's technically legal to use an unholy arrow which costs 1/50 of that to create.
The very expensive lifedrinker greataxe inflicts negative levels on a hit (and also deals negative levels to the wielder -- yikes!).
An evil cleric could also just have a pet wight and let it kill people. Normally wights are human-sized, but you could house-rule a much smaller one that would be easier to hide.