I'm a big fan of .co too.
Tried to buy Surges.com for a long time but was consistently quoted high 5 figures by a squatter. Managed to get https://www.Surges.co off the shelf for $7. Same with https://www.likenoother.co/. Hasn't held me back on anything I've owned.
I would use .co ,io or .me. I feel that .co is getting popular. A good example is https://www.makerpad.co/
most of the other suggestions are good. We chose .org for FootyStats because .org had an authoritative ring to it - that we wanted for a broad stats site.