My favorite for rhyming-it-like-it-is was:

Mary, Mary, quite contrary
How does your garden grow?
With silver bells and cockle shells
And one fucking petunia.

I think most all were like that - just a take on a known rhyme, nothing all new. Maybe I'll remember a few more.

Yes, Opie is excellent and Randolph's Pissing in the Snow has a number, too.