Rings

Blink Ring(AV,22)

The range is unfortunately short, but teleports autobreak grabs. And hopefully once a day is about as much as you'll need to break grabs every round.

Chameleon Ring(AV,16)

Much better after a milestone: free stealth all encounter long for the Ninja. And if you're a Ninja, you'll win that stealth check.

Golden Ring of Teros(AV2,24)

Masters of Defense would be drooling, except this is apparently the one item in AV2 with a conditional bonus to AC that actually typed the bonus. But the daily power may keep your Helm's bonus to defenses going.

Greater Ring of Invisibility(AV2,23)

An Expensive way to replace a level 2 utility power. But concealment for all encounters after the first is nice, so basically it's a Shadow Band with a built-in bonus to stealth.

Ring of the Dragonborn Emperor(AV,15)

Ignore the property, you'll never use that. The daily power though, turns your nicest encounter power, the one you already used (assuming a milestone), into an immediate reaction once a day. Funnier if that power is Hurricane of Blades 

Opal Ring of Remembrance(AV,29)

+2 to Intelligence Attacks. Broken, kthx. What's that, you say it also refreshes Simbarch of Aglarond's encounter power? The only way it would be more broken is if the Fey Charger still worked.

Ring of Free Time(AV2,29)

Yes, I know it's so expensive you'll never actually see one. But ... nice fun nova tricks with Fury's Advance and Soulforge Hammering (And Follow-up Blow and Trip Up and some ways to recover them). And lots of other things just became a lot easier. And heck, I kinda like resist 5 when it's thrown in for fre.

Ring of Fury(D366,14)

More off-action attacks, but as a daily power. Still, Martyrs can make good use of this, especially as it stacks with a backlash Tattoo for three MBAs.

Ring of Personal Gravity(AV1,16)

Pretend to be a dwarf, and a daily power that immobilizes. For will usually be your weak defense, and fort powers will frequently move you. But they'll also frequently knock you prone, which this won't help with. The draw is the daily power: "So sorry, you're not moving." Use this on an artillery, and it'll die quick, even if it's elite.

Ring of Ramming(AV,18)

Increase Pushes by one, but 'spensive. Only interesting if you've got large pushes already, and one square is all you need to go from soft to hard control. (That target number is around 16 squares...)

Ring of the Radiant Storm(AV2,17)

Annoying math to determine your DPR change, but it's about 2 to 2.5 per W, assuming a d12.

Ring of Giants(D378,13)

Free damage on criticals. Better in most cases than a War Ring ... the remaining case for the War Ring is the Guaranteed Crit+RRoT combo.

Ring of Regeneration(PHB,24)

Regeneration 10 is rather low at this level, and if your DM is paying attention, he'll make you spend a healing surge pretty quickly.

War Ring(AV,16)

If you have a Viscous Weapon , crits do another d12. If you have most any other kind of weapon, you'd rather have a Ring of Giants .. and by the time you have +4 weapons you'd rather have the Ring of Gaints even if it's viscous. But ... if you have some way of getting a guaranteed critical, then you'd rather have this. Also, there's no question that a Ring of Giants and a War Ring stack, if you really want big crits, while two rings of the same type might not.