Two of the greatest poets in the 20th century and the first decade of the 21st century took forever to be recognized with the Nobel Prize in Literature. Szymborska received hers in 1996; Tranströmer just this past year (2011).
I’ve thought about both of these amazing poets a great deal in the last few weeks. Until her death in February 2012, Szymborska pursued her art with a clarity few can rival. In Poland, she sells like hotcakes, but she is known by only a small number of poems, proving that strength of work not volume is the key. You can read some of her work at the Poetry Foundation or Poem Hunter.
Tranströmer is still with the world, although he suffered a stroke in 1990 that left him silent. He turned even that into poetry (Grief Gondola, 1996; in English, the Sorrow Gondola, 2010). His awareness of the world and human nuances may be attributable to his profession as a psychologist, but his ability to translate that awareness into poetry is unique. You can read some of his work at the Poetry Foundation or Poem Hunter.