Oh, I love Marianne Moore!
I used to lead off the "First Thing People Notice About Me" section of my OKCupid profile with the full text of "To a Snail" and my current flair on another subreddit is "Utopian Turtletop". As for that poem, "imaginary gardens with real toads in them" is one of those classic Moore lines and I love how she impishly trimmed the poem to almost nothing for her <em>Complete Poems</em>, then included the full version as an "extra." Her sense of erudite play is something I endeavor to live up to.
Thanks for the link to Keats poem. Love it. And seeing it, I recall (and have now found on Amazon) a collection of poems-about-their-forms that I found in my university library years ago. I'll have to see how that holds up.