Moving eyes are not essential to the ventriloquist figure, but placement is critical. It adds to the personality or character of the figure and aids the figure in being able to focus in on what they're looking at or who they're talking too. Here's some tips on the eyes. If anyone would like to add or contribute anything, please email me at gkoepke@mindspring.com.

When I first began investigating the building of puppets, I was in elementary school (and before the Muppets became such a name in puppetry). Seeing a ventriloquist figure is actually a specialized puppet, it seemed logical to me that many of the principals would apply. One thing mentioned in several of the puppetry books I read was that the eyes of the puppet should not be looking straight or centered. The reasoning was that it made the puppet look as though it was staring. Over the years I have seen several quality figures built with eyes looking straight ahead, but it seems that the principle has been followed by at least a few of the major figure makers. Frank Marshall on many of his figures had the eyes towing or looking out and several makers who seem to be in the know have commented that it was an attempt to keep the figure from looking like it had a blank stare. Jack Coats (among many other puppet builders) agreed with the idea of not centering the eyes, at least on the figures he built with stationary eyes, but was concerned that with the eyes towing out the figure could not focus properly when looking at something or someone. His solution was to slightly cross the eyes so it wouldn't appear to be a blank stare and it would be able to focus as well. It was mentioned in the puppet building books and other makers have done this as well. Select the animation upwards and to the left to see the different look a pair of eyes can have with different positions.
Observe other puppets of all types and pay attention to their eye positions. Notice that some do tow out and some do cross. Occasionally they will be looking straight. I have a Coats figure with the fixed, slightly crossed eyes and it's always amazed me at how many people comment on his 'moving eyes'. I think the slight crossing makes him look like he is actually turning his eyes towards me when he is looking toward me and the outside eye is prominant and looking away from me when he is turned away and the inside eye is prominant.
Obviously this is pretty much limited to figures with stationary eyes, but don't rule this out until you try it. I went to high school with a puppeteer named Steve Whitmire (now of Muppet fame) who used plastic spoons on many of his soft puppets. He would break off the handle, sand the edge smooth so it would be semetrical, add a plastic button to make an iris and cover part of the spoon with felt to make an eyelid. It was amazing the expressions he got out of the eyes! Later that year I needed eyes for a small figure I was making in shop class and didn't have the time to install the moving eyes so I picked up a couple of white plastic spoons, broke off the handle, installed a glass iris, and secured them to the inside of the head with plastic wood. I loved the expression and it was a unique look (by the way, I got an 'A' on the project).
A hint... try and get an off white spoon instead of a fluorescent white spoon. You can paint the iris, use a plastic iris, etc. and position the spoons in the head and and secure in place with glue, epoxy putty, or plastic wood.
Ping pong balls have been used for eyes on many figures including those made by the McElroy Brothers, Fred Maher, Ray Guyll, and Verna Finly. Maher would use a ping pong ball and cut or sand a hole in it and use a black marble for the iris. Ping pong ball eyes can be made to move, although I have never done it. You may be able to use the same technology as is used in making the moving eyes out of the fishing bobbers as mentioned in How To Build A Dummy by John Osborne.
Remember those round plastic red and white bobbers that are used when you went fishing? Well they can make wonderful eyes for your figures and puppets. They come in a variety of sizes and are very inexpensive usually costing under a dollar for several (quantity depends on the size) and are usually easy to find in Wal-Mart, K-Mart, sporting goods stores, etc.
To disassemble the bobber, push the little red button on top of the white half. This will push the metal hook out on the red side where you usually thread the fish line. With the hook extended, straighten the wire and then let go of the red button. The button, spring, and wire should all come out leaving a round plastic ball with a hole centered on the white half. Depending on the size of the hole and the size of the plastic iris you can enlargen the hole with a Dremel™ or similar type tool. Glue the iris to the bobber and the eyeball is complete. When the glue is dry, position the balls in the head and and secure in place with glue, epoxy putty, or plastic wood. For stationary eyes you can use either the whole ball or separate the two halves of the ball and only use the white side.
By separating the halves and only using the white side, the eye can also be used on a soft puppet. Take contact cement and glue in a piece of foam rubber on the side opposite the iris, then glue the foam rubber to the soft puppet head.
John Osborne has also used bobbers for moving eyes in some of his figures. Check out his book How To Build A Dummy as recommended on the figure making resources page.
Wooden balls have been used for both stationary and moving eyes. It would actually be easier to name those makers who have not used them than those who have. An iris can be set in or painted on. They are durable and come in a variety of sizes. Sometimes they can be a little hard to fine, but often I have found them in craft stores where they may be sold as 'doll heads' or in a hardware store where they are sold as 'handles'.
Glass eyes have been used in many of the great figures. They've been used for stationary eyes and moving eyes. They do look very real, but it is a matter of opinion as to how real a figures eyes should look. They range in price according to if they are truly glass eyes or the acrylic plastic eyes that look like glass. If there is a draw back, it may be the size limit one may find. From the catalogs I've seen, the largest common size translates to about the size of a ping pong ball and is quite costly. If you compare it to the cost of purchasing a figure, that shouldn't be too much of a problem.