The item level of a piece of gear is Blizzard's estimate of how good the gear is. I've talked about item level before: it's a great way to quickly understand how good a piece of gear will likely be. The WoW UI doesn't show you the item level but a variety of mods will, I have Pawn show me.
Item level is not always a good predictor of item value. It doesn't
include set bonuses. It doesn't value weird items like trinkets or
rings with procs very well. And you can never compare the item level of
a rare item with an epic. But for comparing epics to epics, it's pretty
good
Here's the item levels of various kinds of epic gear you're likely to encounter, along with links to Wowhead searches for those items.
226 Raid drops (hard 25 mans): Kel'Thuzad (Naxx), Eye of Eternity
213 Valorous Dreamwalker T7.5
213 Raid drops (hard 10 mans): Kel'Thuzad (Naxx), Eye of Eternity
213 Raid drops (25 man): Naxxramas, Obsidian Sanctum, Vault of Archavon
213 Emblem of Valor purchases
213 Deadly Gladiator PvP gear (1900-2200 rating)
213 Crafted frost resist gear (leatherworking, jewelcrafting)
200 Heroes' Dreamwalker T7
200 Raid drops (10 man): Naxxramas, Obsidian Sanctum, Vault of Archavon
200 Heroic 5 man drops
200 Emblem of Honor purchases
200 Hateful Gladiator PvP gear
200 Faction reputation rewards
200 Crafted epics (leatherworking, jewelcrafting)
Having done this exercise I'm surprised to see all the epic gear fall out mostly into just two groups. I'm guessing the item level of an item no longer strictly reflects the item budget like it used to. Still, this should at least be a rough guide to comparing your emblem gears, crafteds, and dungeon drops.