How many quests do you feel compelled not to turn in? I see more Images of Arch Mage Vargoth and Magneto Spheres in raids during down time than I ever expected to... and kinda wish I'd saved the items myself. :P

you keep the staff even if you complete the chain

Hmm... now to track down what happened to mine... guess I may have destroyed it, though I definitely don't remember doing so. :P

Not a BC item, but I dearly miss my Keepsake Remembrance, which ensured Ras Frostwhisper was a puny naked human every Skin of Shadow / Alchemy Lab run. Seems though many quest items stay in your inventory upon quest completion these days, only a precious few are actually usable outside their intended zones.

The apple quest from Nathanos in EPL (turns you into a Scarlet Crusade member) is a popular one for stylish Tyr's ganking, erm, "outdoor pvp". Dearly regretted handing mine in, I never did the followups on my Rogue. :) The Staff (Something of Retribution, or somesuch) that the Dragon in Searing Gorge gives you for lighting up the Dark Iron watch towers has much improved my Rogue's Orgrimmar appeal though. Equippable and looks like Hale Magefire, doesn't get destroyed as you hand in the quest.

After Ras got humanized and squashed the first time, I found that the Keepsake no longer did anything. I was sad when that happened.

I have the "repolarized magneto sphere"...I hadn't heard from it before the quest, but right when I was doing the quest I realized that I should never finish it. I've used it a couple of times in public and it seems to be a major attention whore item, whispers/minute is pretty high. But fortunately I don't enjoy the "is that a level 70 druid spell?" or "wow that looks so cool" whispers so much really, it's a bit too much "hey look at me!" stuff. So I'll save it for "special occasions", whatever those might be, and the occasional instance fun. And making fun of paladins is always nice, so magneto sphere + hearthstone is good for a chuckle until people get bored with it.

I also enjoyed the quest in Blade's edge where you get a draenei suit, unfortunately it's only usable in the cave :( And there's also that Netherstorm quest which gives you a similar Blood elf outfit, mine has 1 charge left so I suppose I'm saving that for some "RP event"...assuming it's usable outside Netherstorm.

When you get the Draenai suit in Blade's Edge, you can talk to the mob's vendor, off to the right as you enter the cave. I got an item that lets you turn into a little dragon 3 times and a reasonable fire res cloak, limited availability.

That dragon orb caused much amusement in IF, it took a few minutes of /wave-ing at an acquaintance before they realised I wasn't a pet... :-|

I still haven't turned in "Maxnar Must Die!" for this reason. I know I can still go back there, farm up a suit, and buy another Orb. Can anyone confirm whether or not you can continue doing this after turning in the last quest?

Yes, you can still get the scraps to make a suit after finishing the questline.

The Magnetosphere is the best quest item ever. I'd go so far as to say it rivals even the stalwart favorite - The Furbolg Stick (Dartol's Rod of Transformation).

Then you have the "Furbolg in a Bubble"...