Suppressing evil aura's

[keeper2161]

Is there an item that suppresses an evil aura so detect good won't work? Or that will tell them the person is neutral?

[Zaq]

Minor Schema of Undetectable Alignment and/or Misdirection?

[LuminousWarrior]

Not sure about in 3.5, but in Pathfinder you could get a Ring of Undetectable Alignment. 3000 gp for base price, though perhaps due to roleplay reasons it could be more expensive. Supply and demand. After all, being detected as an undesirable alignment can have fairly negative consequences.

[Necroticplague]

Is there an item that suppresses an evil aura so detect good won't work?
That's....not how Detect Good works. Detect Good doesn't detect Evil auras. It's kinda in the name.

Or that will tell them the person is neutral?
Again, Detect spells don't say a person's alignment.

Anyway, to be more useful on the topic instead of pointing out that you're asking the questions wrong:
An Eternal Wand of Nondetection, while not foolproof, is a strong step in the right direction. A Hat of Anonymity also gives you the spell effect continuously.
An Eternal Wand of Misdirection is more foolproof, but requires you to stick close to someone who isn't evil.

[Elder_Basilisk]

Ring of mind shielding. Undetectable alignment spell. Mind blank spell.

Those are the foolproof core methods that come to mind.

Nondetection and misdirection are good and more generally applicable (at least more generally applicable than undetectable alignment and the ring of mind shielding--mind blank is better in every way but is also 8th level). However nondetection can be bypassed with a caster level check and misdirection can be bypassed with a will save (quick--what save are clerics, paladins, and other people who use detect evil likely to be good at?). Consequently they are of limited utility and should be used only if you are at least as concerned about detect thoughts and other similar spells as about alignment detection.

Undetectable alignment or the ring of mind shielding are what you want to rely on unless you have access to mind blank. For best results, use magic aura to hide the aura on the ring or spell too. People who are serious about detect alignment will also check for spells or items that would block it.

[Crake]

Ring of mind shielding. Undetectable alignment spell. Mind blank spell.

Those are the foolproof core methods that come to mind.

Nondetection and misdirection are good and more generally applicable (at least more generally applicable than undetectable alignment and the ring of mind shielding--mind blank is better in every way but is also 8th level). However nondetection can be bypassed with a caster level check and misdirection can be bypassed with a will save (quick--what save are clerics, paladins, and other people who use detect evil likely to be good at?). Consequently they are of limited utility and should be used only if you are at least as concerned about detect thoughts and other similar spells as about alignment detection.

Undetectable alignment or the ring of mind shielding are what you want to rely on unless you have access to mind blank. For best results, use magic aura to hide the aura on the ring or spell too. People who are serious about detect alignment will also check for spells or items that would block it.

For extra credit, add misdirection ontop of that to give yourself a good aura to anyone who doesnt pass the save DC.

[Goaty14]

I recommend the trusty multipurpose lead sheet (http://www.giantitp.com/comics/oots0281.html). Blocks most dinivations.