There are several options for optics. The simplest and most traditional in design is the AK style side mount -- which is what the scope dirtymike showed you would fit on. A lot of different optics will fit onto those rails, if they have that dropped, left-side attachment mechanism. If you don't have the side mount, your shop can probably install one for you.
For more western/conventional scopes, there are several options. One is the UltimAK style railed gas tube that lets you mount a long-eye-relief type scope in front of the rear sight block. Another is a dogleg type like Texas Weapons Systems makes that rides above the top cover and allows a more traditional scope.
A shop that specializes in AK work will probably be able to show you all of those options.
