Ugly Duckling Presse, a nonprofit press that focuses on publishing poetry in translation, as well as experimental and avant-garde literature.
Wave Books, an independent publisher that focuses on publishing poetry and literary fiction, with a particular emphasis on experimental and avant-garde works.
Omnidawn Publishing, an independent publisher that focuses on publishing poetry, fiction and non-fiction, with a particular emphasis on avant-garde, experimental, and innovative work.
Belladonna* Collaborative, a feminist poetry collective that publishes poetry chapbooks and full-length collections by avant-garde and experimental poets.
Black Square Editions, an independent press that publishes avant-garde poetry and poetics, with a focus on conceptual and experimental works.
It's important to note that many publishers consider experimental and avant-garde poetry, and that it may be helpful to research individual presses to see what they are currently publishing and what they are looking for in terms of submissions.