What Aethien said.
Each different badge can be turned in for a different ilvl of gear. Frost being the best, followed by triumph, conquest, valor and heroism.
There are a couple of items you may want to grab by downgrading emblems (turning triumph into conquest into valor for example),
Idol of Awakening,
Disguise of the Kumiho, and perhaps a
trinket depending on your luck with drops. Some of the druids that geared more recently may have some good ideas as well. Each vendor should allow you to downgrade an emblem 1 tier at a time, however you'll mostly be turning in the triumph badges you get for gear.
But ya, getting geared is mostly an emblem grind, just doing the old 5-mans until you have enough gear to take on raiding. Once you get the 4pc t9 set bonus (the set you can buy with triumph emblems) and a decent regen idol/trinket you should be more than ready to give ToC-10 a try.
Edit:
Just outside of the Crusader's coliseum in Icecrown you can turn in emblems of triumph for ilvl 232 tier 9 pieces (the "Malfurion's" set). They cost either 30 or 50 emblems a piece.
Edited, Mar 21st 2010 11:39am by someproteinguy