Here is a general progression of boots for a DPS Death Knight in Northrend for World of Warcraft.

After you pick up the Chilled Greaves and Spiked Cobalt Boots, your next few options involve Wrathgate and dungeon quests. You may end up higher than level 71 by the time Wrathgate becomes available to you. In that case, you may want to focus on completing Azjol-Nerub and Drak’Tharon Keep. The Enticing Sabatons will carry you from 73 to at least 77, where the The Darkspeaker’s Iron Walkers from Icecrown are almost a side-grade.

The Berserker’s Sabatons at 78 are a nice stopgap if you can find them, but you may just keep what you have until you hit 80. Ultimately, you want to grind out your Knights of the Ebon Blade reputation to Exalted for the Death-Inured Sabatons. However, the crafted Spiked Titansteel Treads are more than adequate as an immediate upgrade when you ding 80.

1. Level 68 Chilled Greaves (1045)
   Obtained by: Quest Reward – The Collapse (Borean Tundra)
2. Level 71 Spiked Cobalt Boots (1194)
   Obtained by: BoE or Blacksmith (5 gold)
3. Level 71 Implacable Zombie Crushers (1221)
   Obtained by: Quest Reward – The Kor’kron Vanguard! (Dragonblight)
4. Level 72 Greaves of the Traitor (1478)
   Obtained by: Quest Reward – Death to the Traitor King (Azjol-Nerub)
5. Level 73 Enticing Sabatons (1651)
   Obtained by: Quest Reward – Cleansing Drak’Tharon (Drak’Tharon Keep)
6. Level 77 The Darkspeaker’s Iron Walkers (1688)
   Obtained by: Quest Reward – Mind Tricks (Icecrown)
7. Level 78 Berserker’s Sabatons (1795)
   Obtained by: BoE World Drop (50 gold)
8. Level 80 Spiked Titansteel Treads (2121)
   Obtained by: BoE or Blacksmith (233 gold)
9. Level 80 Death-Inured Sabatons (2587)
   Obtained by: Knights of the Ebon Blade (Exalted)

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