All this talk about "change addresses" is dangerous. If you don't understand change addresses, you shouldn't be doing anything like this manually. It'd be like someone without an education trying to rewire their fuse-box. I'm sure if you spend some time reading up how to do it, you might get it right -- but also might electricute yourself and/or burn your house down.
In this case, I am the electrician. I wrote Armory to do exactly what is being requested in this thread. It's used by thousands of people, and has been for more than a year. I have figured out all the gory details and put in endless error catching, corner cases, etc, and it's been thoroughly tested. I wrapped it up in a nice GUI that a non-technical user can use safely.
-- Backup your wallet one time. Ever. Period. Forget about change addresses, it's all backed up with your paper backup. Print it or copy it by hand. A digital backup kinda works, but it is encrypted which doesn't help you if you forget your passphrase. You laugh, but this is
by far the most common reason people lose coins -- not theft or hard drive loss. Plus digital backups get corrupted. There's no guarantee it will work when you need it 10 years from now.
-- You create the wallet on the offline computer, and "Create a watching-only wallet" and import it on the online computer. That wallet behaves
exactly like a regular wallet, but without the ability to spend. You can generate and distribute trillions of addresses if you want, and see payments come in exactly as if you had the full wallet on your system... but it actually has no private keys.
-- To send money, create a transaction like you would with a regular wallet, and the "Send" button will instead say "Create Unsigned Transaction". Save it to a USB key, take it to the offline computer, hit "Sign", then bring it back to the online computer and hit "Broadcast".
There's a
tutorial here, which will soon be updated with illustrations and screenshots. Though, most people can figure it out from the in-app hints and that webpage (or from the app, by itself). If you're really starting from scratch, start
at the quick start guide.
Solution for LTC?
There is no LTC version of Armory, but I imagine it wouldn't be too hard for a bitcoin-knowledgeable dev to implement. I can answer questions about it, but I don't have time to actually do it myself. You'd probably have to change some constants near the top of armoryengine.py and modify the C++ utilities to use scrypt instead of double-sha256 for the blockheaders.