The web journal tinywords is open to haiku and micropoetry submissions until June 15th. You can submit right from the web page, and the editor is looking for poems 150 characters or less with a summer theme. (Artwork is being accepted too.)
Neo-Opsis, a Canadian science fiction and fantasy print magazine, is reading fiction, nonfiction, and poetry submissions through August 31st. They don't want simultaneous submissions or previously published pieces, and payment for accepted works is 2.5¢CA per word (up to $125) plus a contributor's copy or two.
With summer pretty much in full force already, here's a Jim Benz poem from DailyHaiku to bring a little bit of winter back.