"I Wandered Lonely as a Cloud" (also commonly known as "Daffodils") is a lyric poem by William Wordsworth and is his most famous work. The poem was inspired by an event on 15 April 1802, in which Wordsworth and his sister Dorothy came across a "long belt" of daffodils. Written sometime between 1804 and 1807 (in 1804 by Wordsworth's own account), it was first published in 1807 in Poems in Two Volumes, and a revised version was published in 1815.

Here is an excellent reading: http://www.poetryfoundation.org/poem/174790

More Info: en.wikipedia.org