World Events

• Elder: complete all the Lunar Festival achievements (every year for 18 days in early February) including honoring every Elder, defeating Omen, collecting the complete festive suit collection, shooting fireworks and firecrackers. (link)
  
• The Love Fool: complete every Love is in the Air achievement (every year on Valentine's Day) including mending broken hearts, obtaining red roses, creating hearts using candies, eating candies, obtaining Peddlefeet, completing both questlines, etc. (link)
• Flame Warden (alliance) / Flame Keeper (horde): complete all the Midsummer Fire Festival achievement (every year for 2 weeks in late June) : descerate every enemy faction bonfire and honor every of your bonfires (link)
• Merrymaker: complete every Winter Veil achievement (every year around Christmas) including saving Metzen, opening presents from under the tree, make seasonal foods and drinks, do the bombing run in BEM as a flying reindeer, snowball faction leaders and other players! (link)
• Brewmaster: complete all the Brewfest achievements (every year for 2 weeks in late September) including killing Coren Direbrew, falling 65 yards while drunk, dance drunk in ridiculous clothes in Dalaran and obtain a brewfest mount. (link)
• The Hallowed: complete every Hallow's End achievement (every year for 2 weeks until November 1st) including visiting candy buckets, killing the Headless Horsemen, eating too many candies, obtain a Sinister Squashling pet, etc. (link)

General

• Champion of the Frozen Wastes: kill all 12 dungeon endbosses in heroic mode and all 3 raid endbosses in 10 or 25-man setup (link)
• Seeker: complete 3000 quests. That is close to the maximum number of quests for both factions. (link)
• Loremaster: complete 740 (alliance) / 580 (horde) quests in Eastern Kingdoms, 765 (alliance) / 715 (horde) in Kalimdor, 568 (alliance) / 685 (horde) in Outland and 760 (alliance) / 835 (horde) in Northrend. (link)
  
• The Explorer: reveal every part of every zone of every continent, even enemy starting zones. (link)
  

Factions

• Ambassador: reach exalted with all 5 capitals of your faction (link)
• The Exalted: reach exalted with 40 factions. There are 54 factions currently in the beta, 11 of that is new to Wrath of the Lich King. (link)
• The Diplomat: reach exalted with Timbermaw Hold, the Sporeggar and the Kurenai / The Mag'har (link)
• Argent Champion: reach exalted with the Argent Dawn and the Argent Crusade (link)
• Guardian of Cenarius: reach exalted with the Cenarion Circle and the Cenarion Expedition (link)

Professions

• Chef: complete all the cooking achievements including doing daily quests, obtaining rare recipes, preparing feasts in battlegrounds, learning most recipes and cooking emotion foods (link)
• Salty: complete all the fishing achievments including fishing up raidbosses and rare fish, fishing from every type of school and winning the STV contest. (link)

PVP

• The Flawless Victor: win 10 ranked matches in a row with a rating above 2000 at level 80 (link)
• Of the Horde: slay all 5 faction leaders of the Alliance (link)
• Of the Alliance: slay all 5 faction leaders of the Horde (link)
• Arena Master: complete all arena achievements including winning a 5v5 game in 45 seconds at level 80, killing someone within 15 seconds of the battle starting, be the last man standing when winning a match and raising your personal arena rating to 2200 in all 3 brackets. (link)
• Battlemaster: complete all the PvP achievements. Various fun tasks in all 5 battlegrounds and in arenas too. Includes the Arena Master title. (link)

The Feats of Strength titles now include the following new titles:

• Conqueror of Naxxramas: realm first kill of Kel'thuzad (25) (link)
• The Magic Seeker: realm first kill of Malygos (25) (link)
• Twilight Vanquisher: realm first kill of Sartharion the Onyx Guardian (25) (link)