[ydant]

Higher end DSLRs (including mid-line ones like the Nikon D7000) support two SD card slots and "backup" mode where both cards are written to with every picture. That's probably enough for most paranoia.

[jacquesm]

One day I will have an original idea. Today is not that day.

[theandrewbailey]

Don't worry. I'm bankrupt on those, too.

[wcfields]

Canon 5D Mk III has both SDXC and CF slots that you can duplicate as you shoot.