If you're going for 2K, you'll want a lot of troops. I generally have about 4 regular plaguemarine squads, then fill up on Havocs or Possessed Plaguemarines to make room for Nurgligns or Plaguebearers.
If you don't have transports or other means of fast movement and good tank hunting weaponry you'll want some tanks, any of them do well, just make sure that you don't take weapons that do essentially the same thing as your Plaguemarines' bolter fire does (ie if you take a Pred, don't bother with Heavy Bolters), you want long range tank hunting weaponry such as Lascannons and the like.
You'll rarely have Fast Attack, as you need many a Rhino, and if you have some Rhinos, you might as well have a lot so that the enemy can't just pick off two or three transports right at the start and limit your mobility. However, it's up to you.
Essentially, the "average" death guard list is an HQ, some Heavy Support, and then just masses of Daemons, Plaguemarines, Havocs and the occasional Possessed or Terminator squad.
It really depends on what you're looking for in a list. Most Death Guard players, such as myself, use the above tried and tested formula, but you can always try other ideas if you want. If you get some new ideas and want input, just come back and ask. If you want to go with the regular old DG army, PM me and I'll send you my Death Guard tactica, which has a large section on troop selection.
