The first thing
I thought of was "Thou Shalt Not Kill" by Kenneth Rexroth. Not exactly about war, but the last lines --
"And all the birds of the deep sea rise up
Over the luxury liners and scream,
'You killed him! You killed him.
In your God damned Brooks Brothers suit,
You son of a bitch."
-- those lines lately have been reverberating through my brain. Sort of falls in line with Dylan's "Masters of War" in my head.
Along the lines of straight anti-war literature: "Dulce et Decorum Est" by Wilfred Owen, which is the most powerful piece of anti-war anything I have ever read. Actually nearly everything by Wilfred Owen; what little there is.
The most disturbing anti-war book I've ever read is Nevil Shute's "On the Beach", which probably falls under the category of obvious. I don't think I'll ever forget reading that book; when I finished it I honestly felt physically ill for a few days.
Also, there's tons of protest songs by the likes of Dylan and Phil Ochs that I think are extremely important, not necessarily because of craftsmanship or originality, but because they phrase anti-war statements in a way that reaches more people than a poem or novel might.