It appears the vendor for the Tier 5 armor has appeared on the beta (like Naxx, Tier 5 will be distributed via a token system), and I gotta say it looks cool. I found all the pictures here (a few classes are still missing at the moment), but I've hosted them here as well in case that resource disappears for whatever reason: Hunter, Mage, Paladin, Priest, Rogue, Warlock.
As a point of reference, I see a lot of** damage and healing* on one of the Priest sets (the Tier 3 set has +483), and that's not counting all the pluses to spell crits, hits, and so on (not to mention filled jewel sockets, of which none of these currently have). The set bonuses are nice as well-- particularly the Hunter's, where only a two piece set bonus gives every pet attack a chance to heal the pet for a small amount. Finally, it looks like the sets are made up of only five pieces each, which means it'll be that much easier to get those bonuses in place (and combine them with other sets that may happen to show up).
So what do you think? I'm not blown away by the stats completely, but there's no question these are extremely nice upgrades, even from Tier 3. And I still think that the Warlock, Mage, and Rogue sets look freakin' sweet.
*Update: Druid dude insightfully points out what I missed: the Priest bonus is for damage and healing, not just healing. I might take back what I said about not being blown away-- that's awesome.
**Update2: My math skills FTL. For specific numbers on how the new sets' +dmg and +healing compare to old sets, see the comments below.