I found this in the Ubuntu Software Center:
I already had Passwords and Keys installed. When I installed the other three and restarted, I got two new icons on the Unity panel and options to encrypt and sign in the right click menu. One of the icons is named Verify Signature and the other is Decrypt File. Clicking on either of the icons appears to do nothing. When I use the right-click menu, it takes a little while but eventually I get a prompt asking me either where I want to save the signature or to which key would I like to encrypt the file. When I sign a file, seahorse-nautilus doesn't clearsign it. It saves the signature as an unreadable .sig file. I haven't tested the encryption option because it won't let me encrypt a file to one of my own private keys.
So, as it stands, I am unaware of a good GUI for GnuPG for Ubuntu.
There's a man coming around and he's taking names.