Let's say I have some coins on an Armory client on an offline computer.
Now I want to keep that computer offline, but would like to spend some of the coins.
What is the most secure way of doing that? I could print a paper wallet of my cold wallet but that will include ALL coins and I would like to use just a fraction of it.
Thanks
Armory supports a watching-only wallet.
Boot up your offline computer and get it to create a watching-only wallet.
You need to get that wallet from your offline computer to your online computer (normally via usb ... don't copy the offline wallet).
If you import that wallet into your online computer, then it can produce transactions for your offline wallet. However, it can't sign them.
Once you have setup the online watching-only wallet, spending the money is (relatively) easy.
Create a transaction and save it to usb.
Load the transaction into your offline computer and sign it. This updates the file on the usb.
Return the usb to your online computer and it will broadcast the transaction.