I face a dillemma here. How do I get the bitcoin client into a non internet connected machine? This is assuming that you can never 100% trust the computer you're using to download the client.
1. Download LinuxCoin ISO.
2. Put LinuxCoin ISO on a CD or USB device
3. Turn off PC (hard for you guys, I know!!!)
4. UNPLUG PC from Network, and turn off any wireless open access points
5. Boot from the LinuxCoin CD or USB device
6. Run Bitcoin Client - a random wallet is created
7. Record the Bitcoin Address (public key) that is displayed in the client. You can write it down, or store it on a CD or USB drive that is "ok to contaminate".
8. Exit the Bitcoin Client
9. Store the wallet.dat file on multiple CD's and a USB device. heck, print it if you want. Virgin wallet files are small enough. These are "NOT ok to contaminate". Never let these touch a PC connected to the internet.
10. Power off your PC. The wallet file Never touched your hard drive (since LinuxCoin is all RAM based).
11. Remove all your media that is "NOT ok to contaminate"
12. Power up your PC as you normally would.
At this point you have a "savings account wallet". Any time you want to put away money for a rainy day, send BTC to the address that you recorded in Step 7. You can verify your account balance or see all transfers via BlockExplorer.
Take your CDs and USB devices and paper, and store them in several safe places far apart from each other. Include instructions for your next-of-kin.
If you are super paranoid, feel free to encrypt your wallet (between steps 8 and 9) , but as others have said, this is risky in that you may forget your pass phrase. My recommendation is that if you encrypt it, you store with it some clues to your pass phrase that only you would know. For instance "My pass phrase is the one I used in 2011. It has 8 words. It has to do with my favorite song and that wench girl who dumped me in 5th grade" (or whatever)
Option 2: If you trust me, contact me, and I'll create for you 2 virgin wallets, each with 2 CDs, a USB device, and a paper printout, using the above technique. One is for you to practice with (maybe with .5 BTC, to make sure you can recover later), the other is your permanent Savings Vault. I'll delete any copies I have, and so if you lose it, you're on your own (i.e. you're screwed). The benefit is, you don't have to worry about the security of my copies. You can randomly select one of the two as practice, to make sure that withdrawal from your "savings account" will be straight forward.
I'll do this service for anyone, for 2.5 BTC (while 1 BTC is in the $20 range), including shipping. If you receive the package un-tampered, you should be safe. Contact me if you are interested.