Many other games make use of Pie menus, and they are quite easy to use. Typically these games are on a console, due to the nature of Analog sticks, but not always; they can be very effective with a scroll wheel. I was reading the
Menu & Interface ideas for 1.2, and drew up a concept of my own in photoshop.
I felt that this should be in its own topic as not to derail his/her topic.
Anyway, enough chat. Heres my concept of how a pie graph could look:

And now for an explanation.
This is a radial pie menu. It would be navigated using the scroll wheel, or whatever the user has bound to prev and next, typically [ and ]. Since there are 8 slices, and they are arranged in a circle, this menu would be an infinite loop type, meaning you can scroll through the list at no end. This also has the advantage that any item on the list is at most 4 away from any other item.
This is what the armory menu would look like.
If this is only stage 1, stage 2 and 3 would be either greyed out.
If the user cannot afford an item, it is greyed out.
The current users balance is in the center, just above the icon.
If an item is grey, it is would be skipped in the scroll index. This is to provide the ability to keep a list organized for visual memory, so one does not have to look at the list every time they want a new item.
The currently active weapon/upgrades are marked with checkmark(s). To sell an existing item, the user selects it and then clicks the mouse button, or whatever is bound to select. The item is now sold, and the checkmark vanishes. The credit balance updates to reflect this change.
To purchase a new item, the user rotates to which item they want to buy, and clicks the select key/mouse button. If there are no conflicts, a checkmark is placed on that item in the menu, it becomes active, and the balance reduces. If that item cannot be purchased, due to conflict, the items it conflicts with flash light white 2 times, to inform the user.
The center area, where the crosshair is, indicates which section is active. Each section has its own icon. The upgrades page has the Plus icon in the center, for example.
Not all items are listed here, notibly absent is the Construction kit. This is because this menu is the descendant of a much broader menu, with only 2 selectable options, at opposite sides of the circle; construction and weapons. Menus with fewer items always will have the same size fields, just only 2 will be scrolled to. Again, this is to preserve visual memory.
If there are more than 8 items to be listed, an more item will appear. The more icon is an elipsis (...)
If an item leads to a sub-menu, it is marked with an arrow (see level 2, 3, and upgrades).
Additionally, if a menu active is a sub menu, as this one is, there is a little X icon in the upper left corner. The user navigates back in the menu history by pressing the backspace key or something similar.
The effects used are relatively simple, and can be controlled via programming. They are limited to outer glows and masks.
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These menus give the advantage of rapid selection of most anything. Teams, classes, buildings, etc, all can be selected using this interface. It allows users to choose items very rapidly with the mouse wheel, almost to the level of convenience and speed of binds.
Hell, this could even be used in a voice command menu, that has been mentioned many times before.
Be ruthlesss, tear into it, but be constructive.