I wouldn't call Rilke non-metrical, and Lorca also frequently writes metrical.
Off the top of my head, Alan Dugan is one of my favorites. His poem
Funeral Oration for a Mouse is one of the best poems I know, and it's not metrical. Stanley Kunitz writes both metrical and non-metrical, and his poem
The Portrait is another top favorite of mine. Philip Levine (who started as a metrical poet) also has some very fine non-metrical poems, though it takes some digging to find them among his overproduction. James Tate also has some very fine poems lurking among a body of lesser poems.