7-Zip uses AES with a 256-bit key. That's pretty good. I use it because the compression is helpful. When I tried using TrueCrypt for general backup, I had trouble fitting what I needed into a 4GB volume, and anything bigger wouldn't be accepted by the microSD card (because they use FAT).
I have a 16GB SD card for backups and it is formatted as NTFS and it has no problems with file sizes larger then 4 GB. My current backup.7z on the card is 6.GB.
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Earth and sky, woods and fields, lakes and rivers, the mountain and the sea, are excellent schoolmasters, and teach some of us more than we can ever learn from books.
John Lubbock