For anyone who's interested in poetry, Villanelle is an unusual poetic structure that's notoriously difficult to write with. I'm interested to see anyone successfully attempt this structure (my own attempt is too embarrassing to post here) or if anyone knows any other interesting poetic forms. The most famous example is Dylan Thomas' Do Not Go Gentle Into That Good Night, which is a plea for his father to not accept death quietly and a brilliant poem. These are the first two stanzas:
Do not go gentle into that good night,
Old age should burn and rave at close of day;
Rage, rage against the dying of the light.
Though wise men at their end know dark is right,
Because their words had forked no lightning they
Do not go gentle into that good night.
This should give you an idea of the structure. The opening and closing lines of the first paragraph are repeated throughout so they have to be potent. There's more information at the wiki. Sylvia Plath did another good one.