The death knight is available to all races on any server. When originally released, death knights could only be made on a server that had a level 55 or higher character on it; this restriction was lifted in patch 3.0.8, and now death knights can be made on any server, provided there is at least one level 55 or higher character on your account.
Note: There is still a restriction to one Death Knight per realm.
As the Lich King did not discriminate when raising those who fell against him, any race can be a death knight.
The Cataclysm races, Worgen and Goblins, are also be allowed to become death knights. Worgen death knights were former followers of Wolfcult, whereas goblin death knights originated with the Steamwheedle Cartel.
[*]Best Race for this stat
[**]Base Health is always 2169, I'm not sure where the health numbers come from, but the "New Health" column is calculated based on:
If Stamina is less than 20:
-Health = BaseHealth + (Stamina - 20)
If Stamina is greater than or equal to 20:
-Health = BaseHealth + 10 * (Stamina - 20)
[***]Tauren receive a +5% racial bonus to their health, which is reflected in the table above.