I always liked the
staff of healing from the BECM game, as well as the humble
potion of gaseous form. Oh, and the
ring of shooting stars. And the
finger nail. And the
crystal ball with ESP. And the
staff of power. And...and why did I ever stop playing that game?!
Good call on the Staff of healing. Forgot about that one! I'd take one of the boots out and add that into my list of top 10. Also, verrry handy to allow the cleric character to be able to memorize more than just any possible heal spell they had access to.
Was in a group where the mage (we called 'em "magic-users" back then ;P ) had a ring of SS. The player LOVED it and used the bloody thing well before the Big Bad we could have (and DM thought we would, use it against!)
Crystal Ball...of any variety, classic. We thought it kinda stupid that you could see people and not hear them, so all CBs in our old group were automatic clairaudience. The ESP one was the "big prize" to find. And the Staff of Power, I believe made my top ten list. So on the same page there.
To add a few more "favorites"...as many have said, the Deck of Many Things, iconic to D&D. The Wand of Orcus, iconic to D&D. Frost Brand, another personal fave and, I think, iconic.
I'd add in there a Deck of Illusions since I saw that used to great story use and combat advantage once upon a time (the player basically modeled their illusionist "witchy style" PC after "Tarot" from the Hellions, "Mirage" of the [then] "New" Mutants of the X-Men comics and "Talisman" from Alpha Flight. She was awesome!).
Hells, we could go on for pages and pages of thread with all of the magic items that have been/make/enhance the feel of D&D.