Terza Rima

The terza rima is a traditional poetic form whose most renowned offspring is Dante's 'The Divine Comedy' (ca. 1300).
Obviously it wasn't first written in English, but it works just as well and is very pleasant in my opinion, especially when it's read aloud/performed.

The form is best written in iambic pentameter:
The sheep was killed by wings of fire and ice;
(the SHEEP | was KILLED | by WINGS | of FIRE | and ICE)

And yes, I know that example is horrible, but it gets the point across

The rhyming scheme is as follows:
a-b-a, b-c-b, c-d-c, d-e-d, e-e

Here is an example from Shelley's 'Ode to the West Wind':

O wild West Wing, thou breath of Autumn's being, (a)
Thou, from whose unseen presence the leaves dead (b)
Are driven, like ghosts from an enchanter fleeing, (a)

Yellow, and black, and pale, and hectic red, (b)
Pestilence stricken multitudes: O thou (c)
Who chariotest to their dark wintry bed (b)

The winged seeds, where they lie cold and low, (c)
Each like a corpse within its grave, until (d)
Thine azure sister of the Spring shall blow (c)

Her clarion o'er the dreaming earth, and fill (d)
(Driving sweet buds like flocks to feed in air) (e)
With living hues and odours plain and hill: (d)

Wild spirit, which art moving everywhere; (e)
Destroyer and preserver; hear, oh hear! (e)

It's a fiddly form, but it's a lovely one and definitely one of my favourites. Give it a shot!