Laul's got some cool desktop calendar papercrafts featuring the Transformers' Optimus Prime & Megatron, Goldorak and Stargate.
2011 Transformers Calendar Papercraft

Megatron is the founder and leader of the Decepticon uprising from the animated series  Generation One, originally known as The Transformers which was aired in United States in the early 80's. This Megatron papercraft was designed by DevianART user monkerum.
Transformers: G1 Megatron Papercraft

A papercraft logo of the Autobots, a group of robots from Cybertron that make up the main protagonists in the Transformers.
Transformers: Autobot Logo Papercraft via papermodel.in.th

Scrapper is the fifth Constructicon. It forms the right arm of the giant robot Devastator.
Constructicon: Scrapper Papercraft

The Constructicon Rampage that appears as a Caterpillar D9L bulldozer forms the left leg of Devastator.

Constructicon: Rampage Papercraft

Mixmaster is hobikitkertas' 4th Constructicon model.  Mixmaster resembles a cement mixer truck and forms Devastator's head.

Constructicon: Mixmaster Papercraft

The third model from hobikitkertas' Devastator series is out! The Hightower in vehicle form is disguised as a truss crawler crane. It forms Devastator's left arm.
Constructicon: Hightower Papercraft

Hobitkertas' second Constructicon model is out. Overload is the red dump truck who transforms and forms Devastator's torso along with Scavenger.
Constructicon: Overload Papercraft

Cerebrave of Indonesia has started the Constructicon papercraft series. Scavenger can transform into a red excavator and combine with the other Constructicons to form the massive robot Devastato.

Constructicon: Scavenger Papercraft

Optimus Prime Update!!! The arms and waist part have just been added. The waist has a total of 13 pages of parts while the arms have 39. This papercraft project sure is massive. 

Optimus Prime Arms Papercraft

Optimus Prime Waist Papercraft

We got two models in one post. First is Omega Spawn (Al Simmons), the main villain in the Image United series and Wreck-Gar, the goateed Autobot from Transformers Animated.
Omega Spawn & Transformers Wreck Gar Papercrafts

Shockwave is one of the robot characters in the Transformers Universe and is usually distinguished by a laser cannon in lieu of one of his hands and his distinctive face, which is featureless save a single robotic eye.
Transformers: Shockwave Papercraft

Rumble is one of the robot characters in the Transformers universes. Rumble's Marvel Comics appearance would use Rumble's red color scheme. Because black coloring in those days usually involved darker inking and dark blues, Rumble ended up looking like a blue robot with red limbs. The model is in pdo format so you'll need to download the pepakura viewer.
Transformers: Rumble Papercraft

Jules has recently finished the 2D part of his Optimus Prime papercraft project.
Transformers: Optimus Prime Papercraft 2D

We have some progress on Jules' Optimus Prime. Part 2B is now ready which means you can now connect Optimus' head to the torso.
Transformers: Optimus Prime Papercraft Part 2B

Here's a little progress in Jules' Optimus Prime papercraft. He just released this torso part which he said is about 30% of Prime's total torso. I sure hope he can finish designing this awesome model.
Transformers: Optimus Prime Papercraft Part 2A

Here's a transformers inspired papercraft from Jonah Penne. Castlebot is a medieval castle that transforms into a battle knight.
Castlebot Papercraft

The Peterbilt 379 was the vehicle form of Optimus Prime in the 2007 movie Transformers. The truck was built by Peterbilt Motors Company, a manufacturer of medium- and heavy-duty Class 5 through Class 8 trucks headquartered in Denton, Texas.
Transformers: Optimus Prime Vehicle Mode Peterbilt 379

Jules has just released the head model of Optimus Prime. He's also having a survey on whether to convert it to a bust or continue to full robot figure. If you were to ask my opinion, I'd love to see it in the same scale as paperinside's Bumblebee. It would be cool to pose them side by side.
Transformers: Head of Optimus Prime Papercraft

I can't believe it's been a year since Claudio released Bumblebee papercraft. To celebrate his birthday here comes the TransParker Bumblebee.
Transparkers: Bumblebee Papercraft