Yeah, look into Truecrypt. It's more than sufficient to keep wifey out of your pr0n.
You'll just set up a large file, whatever size you need it to be, then it will be encrypted into a new volume. When you mount said volume, it'll show up as a new drive letter. Not only will nobody (and seriously, nobody) be able to get into it, it won't even look like a folder or anything suspect at all. It'll just be a big-ass file. There are other, more convoluted ways of stashing stuff with Truecrypt, but for quickness and ease of use, that's a fine option.