Links extracted from http://www.flickr.com/groups/nikon_d300_users/discuss/72157623673342960/

http://www.adorama.com/Als/ProductPage/WVPP160.html
http://www.adorama.com/Als/ProductPage/IESP3000.html 
Any of the recent Netbook computers, paired a USB flash card reader
http://www.dpreview.com/news/1002/10022601hyperdrivealbum.asp
http://www.hypershop.com/HyperDrive-SPACE-s/1.htm 
http://www.digitalfoci.com/photo_safe.html 
http://www.bhphotovideo.com/c/product/644633-REG/Digital_Foci_P23_250_Picture_Porter_35_250GB.html 
http://www.amazon.com/Nikon-MSV-01-Coolwalker-Digital-Storage/dp/B0006283AG 
http://www.xs-drive.com/ 

A verified flash memory of some sorts is probably the safest storage form you can have.
It is simple to put into safe storage (to avoid having it stolen),
there is no moving parts,
it withstands a lot with regard to temperature and other physical abuse.

Simple verify operation:
1. Download WinRar.
2. COPY any number of RAR or ZIP files onto you flash memory – FILL IT UP!
3. Point WinRAR to the root of the flash memory
4. Select all files and directories.
5. Use “Test” (Alt+T)

All files are OK if you get a dialog that looks like this:

—————————
Test finished
—————————
No errors found during test operation
—————————
OK
—————————

Repeat a few times: Reformat the card and repeat the above with a slightly different set of files.
Three or four iterations and you will be about as sure you can be with this test.

I bet there is more advanced tools, but these might require more knowledge and/or hardware adaptions.

Linux users might try “dd” for creating/writing some data, and “md5sum” for verifying it.

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