Q 166: Are there any items out there at level 8 WBL (ideally under 13,500 gp) that either grant immunity or a solid resistance to [Mind Affecting] abilities?
Greater crystal of mind cloaking: This augment crystal grants you a +5 competence bonus on saving throws against mind-affecting spells and abilities. In addition, if you fail a save against a mind-affecting spell or ability, you can choose to reroll the save as an immediate (mental) action. This ability functions once per day. (10,000 gp, Magic Item Compendium.)
Crystal mask of mindarmor: A crystal mask of mindarmor grants the wearer a +4 insight bonus on all Will saving throws. (10,667 gp, Expanded Psionics Handbook.)
These are both decent.
Mindarmor (Magic Item Compendium 13) is a +3,000 gp armor special ability that gives you a +5 untyped bonus to saves against mind-affecting effects as an immediate action 3 times per day.
Commander (Magic Item Compendium 9) is a +2,000 gp armor special ability that gives allies of the wearer within 30 feet (but not the wearer) a +1 morale bonus on will saves. You could put the ability on +1 armor or barding for a skeleton or pet.
A banner of law (Heroes of Battle 133) costs 8,000 gp and provides all non-chaotic allies within 30 feet with a continuous protection from chaos effect. It has to be held in two hands, but maybe you can get a skeleton or trained monkey to carry it. Possession and mental control aren't the entirety of mind-affecting effects, but they're a fair chunk.