You can gpg encrypt a text file or write it down on a piece of paper, but what are other good options to secure your mnemonic seed? I want to hear your ideas :)
You could also scrypt your paper wallet. Then use base64 to get the encrypted data in a printable format. This way somebody stealing it will still need a password to get the keys or mnemonic seed and scrypt will make sure that brute force attacks are infeasible even for weak passwords.
scrypt enc -t120 data.txt | base64 > data.enc.txt
base64 -d data.enc.txt > data.enc scrypt dec data.enc
One major drawback though is that you'll probably have to scan+OCR to get the encrypted data back from paper into a digital format ;-)
The best option I found is:
I bought few of them. This is by far the best option in my opinion.
You might like a more low-tech option: have your seed on a piece of paper, then copy that paper (by hand) and split it in 2 parts. give each part to a different friend. Of course you make sure these friends do not know each other.
You can even do this multiple times, so for example note the seed again on a piece of paper, and give a part of this one to 2 different fiends. Then even if one of the friends falls away, you have a redundant copy of every part of the key.
If you do not trust your friends, then keep part of the seed yourself. There are many variants of course of this, but you get the idea.
Some additional security measures are avaible at https://xmr.llcoins.net/
It includes password protection and two-factor authentication, all while keeping it in seed form.
I like j ust using gpg. Simple secure straightforward. You can store the encrypted file just about anywhere.
I use: https://www.gpg4usb.org
This should not be a computer technology limited answer.
Keeping a few copies of half of the words in some locations and a few copies of the other half of the words in other locations should provide you very good security.
Arguably keeping even a paper wallet (words written on paper) is safer than keeping any computer file in a place it could be leaked onto the internet.
Might also consider Shamir's Secret Sharing for cold storage of a Monero wallet. This is more flexible, secure and resilient than simply chopping up your seed into pieces.