There are books and study guides that explain individual poems, though the poems aren't always very recent. I think Ruth Padel's "52 ways of looking at a poem" and "The Poem and the Journey" provide a useful service. For many years "The North" has had a "Blind Criticism" section where 2 writers comment on a poem without knowing who write it. In "Smiths Knoll" editors sometimes wrote about a particular poem from the issue. The "Best American Poetry" and "Best British Poetry" anthologies have comments by poets, but rarely anything thorough or online.
Here are some places where you'll find online analysis of poems that aren't too ancient -
- Voltage Poetry - poems by Larkin, Jorie Graham, etc.
- Martyn Crucifix sometimes focuses on single poems on his blog. See for example November
- Prac crit is heavy and worthwhile.
- Jim Murdoch frequently posts his poems on his blog, giving the backstory and interpretation
- Kona MacPhee's Perfect Blue companion excellently accompanies the poems in her book.
- Other one-offs are scattered around. Try How I Did It: ‘How to Renovate a Morris Minor’ by Jonathan Edwards