Here is a general progression of plate item belts for a DPS Death Knight in Northrend for World of Warcraft.

The Girdle of Forceful Annihilation from the five-man quest in Dragonblight can be obtained at level 71, carrying you for two levels. At level 73, you can opt to purchase the Girdle of the Howling Berserker from the auction house, or wait a level and run Gundrak for the quest reward Clasp of the Fallen Demi-God. This item will take you to level 78, where you have a few options for upgrades. If you’re not able to run Gundrak, the Rhino-Tail Girdle (a level 76 quest reward from Sholazar Basin) is a solid choice until you hit 78.

1. Level 68 Gold-Plated Coldsteel Girdle (1173)
   Obtained by: Quest Reward – Necro Overlord Mezhen (Howling Fjord)
2. Level 71 Girdle of Forceful Annihilation (1301)
   Obtained by: Quest Reward – Sarathstra, Scourge of the North (Dragonblight)
3. Level 73 Girdle of the Howling Berserker (1408)
   Obtained by: BoE World Drop (40 gold)
4. Level 74 Clasp of the Fallen Demi-God (1598)
   Obtained by: Quest Reward – Gal’darah Must Pay (Gundrak)
5. Level 76 Rhino-Tail Girdle (1383)
   Obtained by: Quest Reward – Rhino Mastery: The Kill (Sholazar Basin)
6. Level 78 Savage Saronite Waistguard (1556)
   Obtained by: BoE (Blacksmith or 50 gold)
7. Level 78 Girdle of the Mystical Prison (1740)
   Obtained by: BoE (Violet Hold or 25 gold)
8. Level 78 Spiked Metal Cilice (1978)
   Obtained by: Quest Reward – Salramm the Fleshcrafter (The Culling of Stratholme)

Prices and links provided by Wowhead. Gear score provided by Loot Rank (based on the PvE Death Knight template).