From personal experience in the past, if I want to store long term then I would use.. *CLEARNET WARNING* Bitaddress.org offline to then generate a address and would then print out the private key and the QR code on to paper and then make sure I store that in a safe place. You can then send Bitcoin to that address and it will be secure. If you are keeping coins in cold storage for a short period then you can even use Bitcoin-QT client offline for short periods. There is always Armory which is pretty much just as good.