Yeah, just looking for a list, pretty much. Please include stuff you can buy as well as unique items (and say which is which). What I've read so far seems to indicate that the best mage stuff you can buy is typically named "Arcane _____," is this correct?

Don't sell stat- and skill-granting equipment; wear it as you see fit.

Boots
Enchanted War Boots: sold at a store, add to Speed. Buy them for every nontechie NPC in your party, too.
Elven Boots: sold at a store, increase stealth. Get an NPC follower to carry them for you.

Gloves
Gloves of Dexterity: +2 Dexterity
Baneful Gauntlets: one of the best items in the game. Murder annoying npcs for free, completely blamelessly, then rez them as needed. Ultimate solution to a LOT of sidequests. Tell your followers to wait and drop the gauntlets near an npc.

Headgear
Dark Helm: +20 Magickal Aptitude, -20 alignment. Found at the castle in Ashbury.

Armor
Caladon Crusading Chain (medium): +1 ST, +1 CN, +1 DX, +1 BE. Useful for stat bonuses.
Smoking Jacket: +20 reaction. Sold at tailors.
Elegant Dress: +20 reaction for ladies. Surprisingly rare; buy one at chargen if playing a woman.
Enchanted Gown: omgwtfbbq good dress, female only. Steal from the seamstress at The Dancing Needle (Black Root).
Dread Armor: very good, very durable armor. Negative reaction. Give it to followers. Warning: your party will look funny.
Various magickal robes: for style, I guess.

Necklace
Jewel of Hebe: +1 BE, +1 CH. Panarii temple, Tarant. Supposedly stealable if you turn the priest around, then stand far away enough to not trigger the alert. The priest does not sleep.
Charming Medallion: gives the ability to cast Charm. Worn by Ristezze in Shrouded Hills.
Finger of SPOILER ALERT: +1 WP, +2 Melee. Found on a quest in Caladon.

Ring
Ring of Influence: +3 BE, +3 CH, +3 Persuasion, +3 Haggling. Worn by J.T. Morat (a gnome) in Grant's Tavern, Tarant. It's a reward for Haggling Mastery, but note that it grants a Haggling bonus, so steal it (perhaps using a Fate point) whether you're going for mastery or not. Best ring ever.
Ring of Shadows: invisibility, hexed, huge damage over time, WILL KILL YOU VERY DEAD. Found at Strange Pond. Highly useful for when you don't have the Invisibility spell. Don't sell it. Use with extreme care.

Weapon
Arcane staff: 80 mana, occasionally sold; carried by npcs late in the game.
Mage staff: 50 mana, often sold, worth buying. Carry several mana sources to exchange when you run out of mana.
That one staff with 40 mana that is found relatively early in the game but I forget where: found relatively early in the game, but I forget where (the first main quest location in Tarant, probably).

Thanks or the response, Starmaker. I'm a bit surprised at some of the items you listed. None of them seem all that good--at least, I was expecting to see higher stat bonuses and/or more items I hadn't already seen in the game. Also, you didn't really mention any robes, which I found odd. Are there just no good robes in the game? I thought I read somewhere about an item called Arcane Robes, which were supposed to be the "best" torso gear for mages, but the post didn't say why.

I had considered the Dread Armor, precisely for it's insane durability (my last set of clothes got broken by successive traps, and I hadn't realized you couldn't get them repaired at shops if they're broken). Is there any merchant who can repair broken gear? Also, what's this about the Dread Armor giving a negative reaction penalty? I didn't think I saw that in it's description. There's a noise penalty (because it's heavy armor, obviously), but where do you check to see if an item will give a reaction penalty?

As I'm a good-aligned character, and I already have 100 MA, I don't think I'll be needing the Dark Helm, but is there seriously no other good headgear for a mage?

There are Arcane Robes (which are golden colored) and there are Arcane Traveler Robes (which are grey colored). The Traveler Robes are slightly better I think. Both of those are good for mages because their stats are very dependent on your MA. So you get really good resistance bonuses because your MA is making sure you get the most of out the bonuses (and you might have noticed Magical items that have stats in parentheses means that, depending on your MA and the "level" of the item, give a percentage of that number in parentheses added to the base stat). Arcane items have both very high bonuses, and very high MA requirements to achieve the full bonus (but 100% MA is definitely enough).

All Arcane items can be found by shopping at the "wise women" and possibly (very rare) at the other magic shops in cities/towns. But the wise women are the safest bet. You just want to make sure you have the money to buy stuff when it shows up.

In terms of reaction penalties: there is never a description that says "oh, this is going to cause a reaction penalty." But you do get different dialogue sometimes and you can look at NPC's reaction in their info box toward you if you wear Dread Armor (or any of the barbarian armors) versus normal clothes.

In terms of helmets: there aren't tons of great mage helmets. Geleam's (I think that is the correct spelling?) Helm is something you can find in tons of magic shops and is good because the bonus stat is really high (+15), so if you have a lot of MA it gives good defense. There is also a Helm of Light, which illuminates the area around your character. There aren't any special hoods or the like though. Other than that I don't think there are any helms that aren't just normal ones (if you want to up your defense stat).

Combat in Arcanum is not difficult, so powergaming is mostly about quests, unusual rewards, and crazy tricks (such as completing two conflicting questlines at the same time, traveling between worlds at will, and fighting a dragon on city streets).

Skills, stats (where stat thresholds are concerned), rep, spells and schematics matter. Enhanced damage resistance doesn't. It can save you in a particular instance of a fight from unlucky rolls, but it doesn't make unwinnable fights winnable.