Terran already has a thread over at desarrisc's awesome Analysis of Terran Weaponry, so I thought, why not give Protoss some love? <3
Feel free to discuss Protoss technology here!
No one's really an expert on fictional alien technology, so I'll go by the lore and what's going on in-game to study these as best I can!

Stalker <-- finished! clicky
So I'm going to start with one of my faves...
The Colossus
![[image loading]](http://images1.wikia.nocookie.net/__cb20101202053326/starcraft/images/9/92/Colossus_SC2_Cncpt2.jpg)
Just look at this beautiful towering behemoth of death. Simply stunning!
As in the lore, this is an ancient Protoss war machine, a highly intelligent robot strider built to support Protoss armies. But what makes this baby tick? Let's take a look inside.
The entire thing is powered by a primitive Protoss engine of some kind, as evidenced by the lack of blue beams. The Colossi's power lines however, show the trademark blue energy coursing through its giant body. A standard Protoss engine has a pylon-like crystal core that directly produces the perfect blue beams seen in all Protoss weapons. From this we can see that for the Colossus, the crystal does not produce the beam directly, it powers only the body of the Colossus. The Thermal Lance is a secondary function created from within the body of the Colossus, burning an internal supply of vespene gas to shoot raw beams of fire, rather than firing standard precision cut blue beams. The Protoss are genius to design the firing mechanism to concentrate its fire into a beam, wasting less energy and putting more power into every shot.
Why this design? Well it appears that due to the size of the Colossus, the energy consumption just to keep it running is pretty high. Remember, we're talking about a machine tall enough for airplanes to attack head on. Thus, the power core cannot support both the Colossus and its lasers at the same time, so no blue lasers. The Colossus saves a lot of energy by using an older Protoss engine (most likely a cold fusion reactor of some kind) to ignite many foes at once with searing fires of vengeance.
![[image loading]](http://wiki.teamliquid.net/starcraft/images2/8/81/Extended_thermal_lances.gif)
The Extended Thermal Lance, at the cost of 200/200, augments the Colossus with a stronger firing cannon to control the powerful blast that comes with a longer beam. It is assumed from the cost that the engine within the Colossus is also improved, supporting the constant production of the longer beams through the burning of additional vespene.
Also note that the Thermal Lances are external, allowing for more efficient cooling due to the intense fiery heat generated by non-psionic beams.
![[image loading]](http://wiki.teamliquid.net/starcraft/images2/6/67/Cliff_walk.png)
With 4 legs, stability is not an issue for the Colossus, able to navigate terrain and scale cliffs with ease. The thin legs are stronger than they look, forged with that famous golden Protoss metal plating. So pretty!
Now let's zoom in on that lovely face.
+ Show Spoiler +
The Colossus appears to be armed with an array of optical sensors and an additional smaller beam firing mechanism. The uncommonly high amount of sensors on the face of Colossus is simply the result of older Protoss technology. The many sensors make up for the lack of any pilot, and the Colossus is intelligent enough to determine which targets to attack on its own without any Protoss command. Its four large eyes (optical sensors) aim the beams of the Thermal Lances, pinpointing the area to be fired upon. The smaller protruding structures have eyes on the tips, and appear to be for surveying the landscape, as they can move independently like a chameleon, without the Colossus needing to turn its head all the way. This means the Colossus has excellent vision, able to aim without fail and be aware of its surroundings.
It also has a small beam on its little head, which can be seen when staring at the Colossi's portrait animation long enough. Though it seems to be too weak to attack anything, it looks like it is merely a windshield wiper, clearing debris or any unfortunate creatures obstructing the Colossi's sensors. This would be perfect as covering the sensors of a Colossus would rend it useless and unable to aim. The small head beam fixes this flaw and eliminates the problem entirely. Protoss genius at it again.
