I've done a lot of reading trough D&D books last few days and I noticed several items stand out in usability and most of my chars have them. What are good and not too costly items you just gotta have ? I list D&D stuff, but any setting items are ok to mention, as long as you provide brief explanation.

Decanter of Endless Water (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. Cool off hotheads at taverns. Endless usage :P

For all those sneaky characters out there the Collar of Umbral Metamorphosis from Tome of Magic is definitely a must. For 10,800gp you can gain the Dark creature template for 10 min a day.

In addition to such goodies as +8 Hide, +6 Move Silently, +10 ft move speed (all unnamed), cold resistance 10, superior low light vision, and Darkvision 60ft, you even get the ex. ability to Hide In Plain Sight which is the real winner.

If you need more than 10min/day, you can have a continuous collar for 22,000gp. Just sick.

I'll list more later... your turn.

I've always seen the "Ring of Sustenance" as a must have for any character who has an extra 2500 gp. It provides nourishment in the way of food and water, as well as allows the character to gain the benefit of 8 hours of sleep in a mere 2 (great for spellcasters ). I almost feel like the 2500 gp price tag makes it a steal of a bargain.

I always found a Ring of Freedom of Movement to be a necessity.

For lower level characters a ring of feather falling is just to good (the potential to avoid 20d6 damage, as well as providing several additional escape options due to not having to worry about before mentioned damage)

I can see why ring of Freedom of Movement... Crapload of protections - from paralysis, Solid Fog, Slow, and Web to name but a few effects. It also makes you immune to grappling, which is really, really nice for 40.000gp

I always found Ring of Susteinance to be dumb item to have... Nice bonuses, but no need for food or drink ? Lame to play.

Hm... Rings seem to take the cake for now.
Let's see what I can find that is NOT ring.

Complete Scoundrel holds item my DM asked a LOT of money to make using only core books... a must have for any party that expect to be separated at one or another point of the game (any non-dungeon crawl :P )

Aspect Mirror, 4000 gp/Mirror. - The mirrors are magically attuened to scry on the location or owner of any of the other in the set (Up to 5.) Standard action to activate you can scry and hold a two way conversation with someone holding the other mirror, and there is no limit on uses.

20000 for the ability to talk to your entire party of five pretty much infinetly provided they remain on your plane? I'm sold.

you know, I thought the same thing...and then I was informed that even though you get the benefits with just 2hrs sleep, that spellcasters STILL need 8hrs of rest/meditation to regain their spells

For a mid-low level spellcaster, wand of magic missle. Give you 50 shots of always hit, makes your damage dealing capabilites much more standard, and allows you to memorize more "useful" spells.

Hmmm... Magic missle wand is too dependent on caster level, and as such, does not come too high up on bargain list for me.

As far as wands go, I'd say Wand of Vitality, lesser takes the cake
That's like 550 Hit points cured for price of 750gp... Drawback is that it is effective only when you have lots of time free to cure yourself... Useless during encounter.

Wand of Lesser Vigor. 11 HP cured per charge...total of 550 HP healed for 750 GP...oh, wait.

Was that the one you meant?

FH 1 isn't too good in combat, no, but it's da bomb right afterwards.

For me, a ring of sustenance is possibly the most useful non-combat item in the DMG. Aside from the weight it saves, it means you don't need to be asleep (and thus at a disadvantage to attackers) for as long. Let the wizard and cleric get his eight hours, the other three or four party members can crash one at a time, with two or three people standing guard at all times.

It also completely avoids any chance for someone to poison you through food. And yes, this has come up in a game I've played.