Argent Dawn no longer, Argent Crusade takes over. Well, add a Order of the Silver Hand into it, mix with Battle for Light's Hope Chapel (Dark Knight final quest event, really nice one). Argent Crusade can be found at Argent Vanguard (Icecrown, place will change dramatically after you finish the quests in there) and in Dawn's Reach (Dragonblight), Light't Breach (Zul'Drak and The Argent Stand (Zul'Drak).

Quartermaster Veteran Crusader Aliocha Segard is at Argent Vanguard in Icecrown (at highest located set of  tents). For reputation rewards look at The Argent Crusade in WowWiki.

Reputation raising :

• Slaves to Saronite (250 reputation) from Absalan the Pious at Skybreaker (Flying ship)
• Pa'Troll (350 reputation) from Commander Kunz at The Argent Stand (Zul'Drak)
  To complete Pa'Troll, complete one quest from each of the four quest givers:
  • Captain Brandon:
    • Troll Patrol: Can You Dig It?
    • Troll Patrol: High Standards
    • Troll Patrol: Something for the Pain
  • Captain Grondel:
    • Troll Patrol: Couldn't Care Less
    • Troll Patrol: Creature Comforts
    • Troll Patrol: Whatdya Want, a Medal?
  • Captain Rupert:
    • Troll Patrol: Done to Death
    • Troll Patrol: Intestinal Fortitude
    • Troll Patrol: Throwing Down
  • Alchemist Finklestein
    • Troll Patrol: The Alchemist's Apprentice
  • Congratulations! (if Troll Patrol was completed quickly enough - within 20 minutes) (350 reputation)