"Watch your step, please...it's a little cluttered down here. I really need to get my shop goblins to give this place a good cleaning. If you're looking for...well, stuff...this is the place. Magic items come in all shapes and sizes, and most of them can be found down here...somewhere...if you're willing to dig deep enough!"Defensive
Anklet of Translocation (MiC 71, 1,400 gp): Allows two 10' teleports per day. Excellent for breaking grapples.
Cube of Force (DMG 253, 62,000 gp): Not cheap, but it can protect you against everything. That's worth the big bucks.
Offensive
Bead of Force (DMG 248, 3,000 gp): 5d6 damage plus Otiluke's Resilient Sphere.
Crystal of Return (least) (MiC 65. 300 gp): Feats are expensive. Effectively buying the Quick Draw feat for 300gp--that's a bargain. The lesser version is a good buy, too, at 1,000...the ability to call your weapon to hand from up to 30 feet away is worth much more.
Dust of Sneezing and Choking (DMG 275, 2,500 gp): The fact that Dust of Sneezing and Choking will stun the opponent even if they make their saving throw makes it deadly--so deadly that it's likely to be banned in many campaigns. If not, take advantage!
Scabbard of Keen Edges (DMG 266, 16000 gp): Gives Keen to any weapon it holds.
Truedeath Crystal (lesser) (MiC 66, 5,000 gp): Gives the weapon the Ghost Touch ability for much less than it would cost to add the ability to a high-powered weapon. The greater variant, at 10,000 gp, allows sneak attacks on undead--also highly valuable.
Utility
Candle of Invocation (DMG 251, 8,400 gp): Somebody seems to have forgotten about the 1,000 XP price tag on the "calling creatures" usage of the Gate spell. Since this item is at CL 17, you can call a 34 HD monster and control it for 17 rounds.
Decanter of Endless Water (DMG 254, 9,000 gp): The Decanter has a thousand uses beyond just providing drinking water. Put out fires with it. Use it as a jet propulsion system for a small boat. Create sophisticated hydraulic technologies using it as a power source. Combine it with Water Walking to produce an instant bridge.
Enveloping Pit (MiC 159, 3,600 gp): If you're Lawful Neutral, Lawful Evil, or Neutral Evil, this is a Portable Hole--only with more than five times the normal volume, at about a fifth of the normal cost. Just make sure you stick a ladder in so you can get to the bottom easily.
Heward's Fortifying Bedroll (Complete Mage 132, 3,000 gp): Allows casters to regain spells with only one hour of sleep, rather than the usual 8.
Heward's Handy Haversack (DMG 259, 2,000 gp): Holds less than a Bag of Holding, but also costs less, and the retrieval function is very valuable.
Ioun Stone, Gray (DMG 260, 25 gp): With continual flame, becomes a hands-free perpetual light source.
Ioun Stone, Orange (DMG 260, 30000 gp): +1 caster level.
Aspect Mirror (Complete Scoundrel 113, 4000 gp/Mirror): Provides a reliable means of communication between party members. Can also be used as a highly effective "closed circuit" camera system.
Quaal’s Feather Token – Tree (DMG 264, 400gp): If you can't think of uses for an instant tree, you're not trying very hard.
Quiver of Ehlonna (DMG 265, 1800 gp): Nice for arrows, nicer for wands and staves. The Artificer's best friend! It's not a bad idea to create it in a non-standard form, if permissible, to prevent smart enemies from sundering every quiver they see.
Silent Portal Disk (350gp, Magic of Faerun p165): Any door you put the disk on makes no sound, no creaking when you open it, no cracking if you smash the lock. Your DM will hate your rogue. If you cast "animate object" on the door, you will have the first door ninja ever. You could also whack people with the door and the hit wouldn't make a noise.
Survival Pouch (Races of the Wild 173, 5,000 gp): Provides you transportation, hauling capability, food, instant campfire and/or torches, shelter, water, rope, shovel, bow & arrows.
Tooth of Savnok (Tome of Magic, 2000 gp): Move at your normal speed even when wearing medium or heavy armor or when carrying a medium or heavy load.
Class Specific
Badge of Valor (MiC 208, 1,400 gp): Allows a bard to increase the bonus granted by his Inspire Courage ability 3 times per day.
Boccob's Blessed Book (DMG 249, 12,500 gp): Contains 1,000 pages. Does not require the user to spend the usual 25gp per page materials costs. You pay 12,500gp for 25,000gp worth of spellbook. The portability is a bonus.
Demolition Crystal, greater (MiC, 6,000 gp): The sneak attacker's bane is creatures immune to sneak attacks. The Demolition Crystal allows sneak attacks on constructs, gives a damage bonus, and causes the weapon to be treated as adamantite for purposes of overcoming damage reduction.
Hide from Undead at will with no save, even for intelligent undead.
Robe of Mysterious Conjuration (MiC, 10,000): Sacrifice a spell slot to cast an equal level Summon Monster spell, kind of like a Runestaff loaded with the summon line only it comes with free Rapid Spell built in.
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