Since I mentioned Morgan in a previous thread, I'll nominate his Collected from 1990.
At 600 pages, the Collected only spans the first 70 years of the man's life and leaves out many, many poems. There are also the 20 years of poems he wrote after the Collected. Nor does the collection include his translations, which are numerous, and which are compiled in a different book, also several hundred pages and incomplete.
Morgan wrote in every style imaginable: concrete, sound, sonnets, limericks, vast expanses of free verse, one-word poems, ottava rima, sestinas, collages, found poetry, emergent poems, and bunches of nonce forms.
Morgan can be considered a great poet for many reasons, maybe the most important one being he loved language and playing with words.
And since Mr. Morre mentioned Basil Bunting in the previous thread, check out Morgan's elegy:
A Trace of Wings