I'm concerned about the security of the files on my laptop should it get stolen.  We seem to be getting regular reports in the news of sensitive files, that weren't protected, getting stolen.  There's also the danger of someone accessing sensitive files via the Internet. 

I know that individual programs can encrypt individual files, but this tends to be time consuming inputting passwords for each document you work on. 

I have a lot of scanned images on jpg and pdf files that I would  like to view as thumbnails.

Would anybody have a convenient approach to encryption for files on your disks and memory sticks  they'd like to share?

If you're using Windows, trucrypt is usually touted as the best choice. 

http://www.truecrypt.org/

It can encrypt selected directories or your entire disk.  Just keep in mind that while encrypting the disk may seem convenient, it is more complicated and will decrease the performance of your laptop slightly.  Since every file is encrypted, every file must be decrypted before it can be read.  Modern processors can do this fairly quickly, but there are a lot of files that windows reads frequently and you will probably notice a slight slowdown.

I've never used it myself.  I tried a few times, but something about the particular processor I had at the time didn't work with it.  My whole computer would crash and reboot every time I tried to encrypt a file.  But, I've heard from a lot of people its the best program out there.

I'm not sure what kind of sensitive material you are worried about protecting.  *Most* laptops that are stolen are taken for the hardware.  Simple thieves just want to sell the stolen laptop to make a buck.  They don't care what's on it.  Proper (strong) password protection alone is often enough to make it not worth their trouble, and they will simply reformat the disk without going after the data.

Also, disk encryption isn't the best solution if you are concerned about someone breaking in through the Internet, especially if you use whole disk encryption instead of encrypting individual files or directories.  Since the encryption key is sitting in memory while the computer is on, if someone gets access to your computer while it is running, they will have access to your files.  Proper passwords, firewalls, and virus scanners are much more effective at thwarting a remote attack.

I'm not trying to discourage you from using disk encryption - it is a good measure to take for sure.  My point is that you should ensure the basics are taken care of before you move on to encrypting your files.

Depending on the age of your hardware, if supported I'd use Microsoft's BitLocker. It's relatively easy to set up, takes a while as it encrypts the entire drive, and is doesn't produce as large of performance hit as other encryption software. The reason I recommend it is because BitLocker requires a system startup PIN to be entered, if the pin is not entered or incorrectly entered 3 times, the whole drive becomes inaccessible until unlocked with the appropriate key code (assuming you backed it up when you created it).

http://mt5.radified.com/blog/2010/02/ciphers-keys-encryption-algorithms-rijndael-truecrypt.html

I use Truecrypt, which MrMagoo mentioned.  You can create a "container", which is a large, encrypted file to the outside world, but can be mounted as a separate drive letter in Windows to access the container's contents.

The container file is on my laptop HDD and my Startup folder contains a shortcut to Truecrypt so that when Windows boots a dialog box pops up asking for the container's password.  I put in the password and have chosen to have Truecrypt mount it as drive T:.  From that point on, you access files just as you might any external HDD.

Truecrypt can optionally encrypt the entire HDD, but I don't care if Windows is encrypted.  I only use it for my private, personal stuff.  If my laptop is ever stolen the thief would still be able to boot Windows but wouldn't have access to my personal files.

Also, by encrypting a small container instead of the entire HDD, I can copy that container to a flash drive.  (Note you can have multiple containers.)