I've recently written a few sonnets with Petrarchan rhyme schemes, but with varying line lengths. Some of the patterns I've used (# = beats per line; / = stanza break):
3-4-5-3 / 3-4-5-3 / 3-4-3 / 3-4-3
4-5-5-4-4-5-5-4 / 3-5-3-3-5-3 [still on the met board
here]
4-5-5-4-4-5-5-4-2-2-5-4-4-3
I've also done a pure pent sonnet with this rhyme scheme:
A B B A A B B A A B B C C C
Since they're mine, I can't post them (except for the one still on the board here), though I'm happy to PM them. In general, I've really enjoyed trying out the heterometrical forms—I think all three are among my better poems. I think the rhythmic variation helps them to sound fresh, while still possessing many of the virtues of traditional sonnet forms.
The pent sonnet with the nonce scheme is from an earlier period where I was more old-fashioned. I think it's the best poem I ever wrote in that style (in part because I think the variant rhyme scheme served the poem well), but it's still more of a dead thing than a living. I'd like to write another with that pattern, someday.