The Minecraft Armour Stand Swapper is a compact redstone design, functioning in the current 1.8 game update. The redstone contraption is capable of holding up to 5 armour stands due to Slime Blocks bounce height. This has a lot for every suit of armour in the game (Leather, Iron, Chain, Gold, and Diamond). Size: 6x5x10

With very little effort watch as your armour stands toggle, simply by rotating an item within an item frame. A demonstration has been provided below:

Step 1: Materials:

For this build you will require:

2 Sticky Pistons
1 Slime Block
13 Redstone
5 Redstone Torches
4 Redstone Repeaters
1 Redstone Comparator
3 Iron Trapdoors
1 Wooden Trapdoor
2 Halfslabs
1 Itemframe [+One place-holder item (of your choice)]
1 Noteblock/Furnace/Obsidian [Immovable Block]
1 Cauldron [+one Water Bucket]
About 33 Full blocks for building on.

Step 2: Layer by Layer Construction [GIF]

Building:

Images [From Bottom Up]:

1 Sticky Piston, 2 blocks
1 Slime Block, 1 Redstone, 1 (Redstone) Repeater, 1 Block
1 Redstone, 1 Noteblock, 1 Iron Trapdoor
1 Redstone, 1 Repeater [3 ticks], 2 blocks
3 blocks, 1 Redstone Torch
7 blocks, 2 Half-slabs, 1 Redstone Torch, 8 Redstone, 1 Iron Trapdoor
1 block, 2 Redstone Torches
1 block, 1 Repeater
2 blocks, 1 Redstone
1 block, Redstone Comparator [Inverted]
2 blocks, 1 Redstone, 1 Redstone Torch
1 Repeater, 1 Cauldron [Filled with water]
1 block, 1 Sticky Piston (Upside down)
5 blocks, 1 Wooden Trapdoor, 1 Itemframe [+1 Item]
DONE

To insert Armour Stands, simply place them upon the trapdoor (clicking two blocks above works) and rotate the item in the item frame. If the design has been built correctly it should process the first armour stand.

Step 3: Important Things to Note:

Do not forget about the timings on the repeater, and that the comparator must be inverted
Trapdoors may pop off in initial stages of the build- don't worry they can be reapplied later.
The cauldron must be filled.
Use half-slabs where shown- otherwise is could cause some unwanted issues later/break the device.

Enjoy~!