I thought this would be a good time to start participating in the FTW Collaborative posts. My must-have unit has to be Plague Marines when playing Chaos. Not only is the fluff and models great, the rules aren't half bad either. My love for Plague Marines started back in 3rd edition with the codex having Nurgle-specific rules(I miss the Legion specific rules). Now, when playing Chaos I always try to squeeze in two units of 7 Plague Marines riding in a rhino. Usually, one of the units has 2 meltas, a champion with powerfist and Icon for deepstrikers or daemons. The other unit is usually the same with the exception of having 2 plasmas. I find these units work great for many roles. They can sit on nearby objectives, race to further away objectives, and doubleteam with other units from the army(like Khorne Berzerkers) to make a formidable one-two punch. Plague marines being T5, Fearless and Feel no Pain makes them very hard to remove from cover unless your opponent dedicates a sizable portion of his army to remove them with lots of shooting or a very good assault unit(Blight Grenades help against these).
Below are some pictures of the DeathGuard army I have been cataloging on this blog. I have recently been working on other projects instead of painting this army. I want to get back to the painting, but now I'm living with my mother-in-law(so not as much space as really needed for my painting) and my 19 month-old daughter loves my models, so very difficult to paint while she is sitting on my lap playing in my brush water.
I hope to get in on some more of these collaborative posts in the future. This was fun just talking about I unit I do love to see hit the tables. Soon I hope to be posting some things I am building for my ever-growing Space Marine army.