In collecting Plague Marines for use in Chaos Space Marine and Death Guard armies, I can strongly recommend also purchasing a boxed set of warhammer fantasy zombies for conversion work. A number of examples of the use of zombie parts can be seen throughout this blog (e.g. Plague Marine squad).
In this posting, I want to draw attention to the use of zombie parts for chaos marine backpacks. This is a modestly simple conversion to execute and I think makes a plague marine stand out from their brethren more than usual.
I've taken a standard chaos space marine backpack and lopped off the exhaust vents. The struts that would normally support the vents have been completely removed and filed down.
Using a pair of zombie hands (from the zombie standard), I have then attached (pinned to be precise) two hands where the struts were previously located on the backpack and glued the vents underneath them, suggesting that the hands are now the thing responsible for holding them. I then attached some twisted wire to the terminus of the vents and connected them up with the body of the backpack (the yellow and silver painted portions dangling off the vents in the image). As a final step, some grit (fine sand) was glued in to place around the edges of the backpack to make it more Nurglesque.
A variant of this is to turn the hands up-side-down so that the vents are held upward by the hands -- I've seen one person do this, but I think the downward hands looks better myself.