However, there seems to be no real solution. Almost every solution i have encountered needs a computer side client to unlock the client on the drive.
What I would love is a way to just plug in the drive, let the window pop up which tells you it is locked and it needs a password. Put it in, and the window gets unlocked.
If you have no computer-side client installed, then what exactly do you expect this "pop-up window" to be displayed by??
Basically there's no such thing as a "simple lock" - you need to have everything on the drive encrypted, either with a "container" like TrueCrypt (or similar), or a "filesystem" like eCrpytfs (or similar).
I believe you can get external USB HDs where the encryption is all done by the drive-controller itself, in which case you wouldn't need client software, but these are usually very expensive.
After some googling I found http://blogs.computerworld.com.....ard_drives