I recently discovered the XPAN 65:24 aspect ratio. It's super wide, but it has a certain look to it. It's a challenge to imagine how best to compose with such a wide format, but I think when you get it right the results have some real impact. Best viewed on a wide-screen monitor of course (it doesn't really work on a smartphone!).
The Panasonic S5 that I'm now running has 65:24 as one of its selectable framing or cropping options so you can more easily preview it in the viewfinder. You can get the final result by cropping a single shot of course, but if you do two shots in regular landscape format side by side and stitch them together later then you'll get a higher res result.
Anyhow here are a few shots to kick it off. Will be interesting to see if anyone else wants to play!
The Last Gasp of Sunlight by Paul Kaye, on Flickr