Here's what I did to secure my wallets:
1. Installed Dropbox on home/work computers.
2. Installed Truecrypt on my home/work computers.
3. Created two different Truecrypt containers, each one only 2 megs in size.
4. Placed the encrypted container files inside of Dropbox.
5. Mounted the first container on drive Z: and moved my wallet.dat from my work computer into it (after turning off the bitcoin client, of course).
6. Dropped to a command line and used the "mklink" command to create a symbolic link between the wallet.dat file inside the Truecrypt container and the wallet.dat pointer in my bitcoin user data folder. Note: If you want to store *everything* in your encrypted container, and not just the wallet, you can alternately just run "C:\Program Files\Bitcoin\bitcoin.exe -datadir=Z:\" when launching the Bitcoin client, but I like to just symlink the wallet file so the encrypted container can remain small and lightweight inside of Dropbox.
Now, whenever I want to open one of my wallets, I just mount it's corresponding container using Truecrypt and launch Bitcoin. Using this method, I can very easily and securely switch between multiple wallets from multiple computers. I can mount my work computer's wallet using my home computer and vice versa. As soon as I'm done with whatever transactions I need to do, I turn off the Bitcoin client and un-mount the wallet container.
If you want to keep the Bitcoin client open and running (so that it is always up-to-date with the block chain), just create a new, blank dummy wallet and corresponding container and mount that. Just make sure that you don't ever store any BTC in it or actually use it for anything, since it will be mounted at all times and if your machine was compromised someone could easily send out any money stored in it.