Most of the modern companies still focus on historical military settings (Romans, WWII, Civil War, etc). There are few modern sets (Armies in Plastic is delving into this area), and I would love some Vietnam and Korean War era playsets as well. Only Barzso licensed a playset in the last 10 years - The Last of the Mohicans Playset was amazing.
Treehouse had a great set of "Aliens" plastic figures, including a playset of the atmosphere processor.
Anyway, without licensing tie ins, there just aren't any 54mm army men playsets or figures coming out...
...but wait, slowly but surely, Skybound comics and Gentle Giant are building a zombie army around the very popular Walking Dead comic book.
The first figure set was the sword wielding heroine Michonne with her two zombie pets, including real chains to leash them. This was released as a 2012 San Diego Comic Con (SDCC) exclusive.
A few months later, Gentle Giant released a 14 figure zombie horde pack. There are seven poses, molded in two colors, light green and brown. The packs were sold out on the Gentle Giant website almost immediately.
For SDCC 2013, three figure packs were released as exclusives with each pack having a main character figure and a zombie figure. These sets included Rick Grimes + zombie, his son Carl Grimes + female zombie, and f-bomb dropping bad guy, Negan with his barb wire wrapped baseball bat Lucille + zombie. These were released by Skybound, the comic company that publishes Walking Dead.
Also for SDCC 2013, one of the zombie horde figures was recast in blue plastic and painted with blood spatter to simulate the prisoners in the prison story line prevelant in the comic book and television show.
So what's next? Who knows? I could see more comic con exclusives. Would love another zombie horde pack with more character figures.