I did a few modifications to my Rostock Max. Most of them are inspired by some of you guys - thanks for your input!
I'm not sure if every of this upgrade is necessary to get a better print quality, longer machine lasting or better operation - I just like handicraft work

Let's get started!
Lights
The wires are going through one aluminium rail. Extruder stiffener
Made of an allen wrench - I have plenty of them due to Ikea

Now it's possible to adjust the position of the gear, so it is in the center of the two other gears. Connectors
I added 2 pairs of D-Sub connectors for easier removal of the extruder-unit. One is for the hotend the other one for the extruder stepper. The connectors are screwed together for save operation. Emergency switch
It is connected to the green wire of the PC power supply and switches off the power for the stepper motors (and hotend). Switches
The small one switches the lights the large one the power to the heatbed.
I also screwed the LCD face plate above the display to the LCD standoff plates. The screws are going through the holes in the PCB of the display. I added a nice aluminium knob. Heat sinks
There where places to put heat sinks on the backside of the Rambo, so I put some there

I added some aluminium foil to the back of the Onyx to minimize heat radiation. Table insulation
I added also some aluminium foil to the top of the table. With this two foils I could significantly increase the heatbed temperature (with the original underpowered power supply).
You can see in the picture also a small chamfer for the wires and how I soldered the wires to the back of the heatbed pointing inwards. Automotive fuses
I replaced the fuses for the heatbed and hotend with automotive ones. Aluminum heat dissipator plate
Like Mhackneys, just without the cutout for electronics pads. (Because I soldered them to the back side.)
Got it for 10€ water cut from a local. It was important to be precise with the holes for the screws, but because there are six of them, it was easy with a pair of compasses.

I replaced the screws with metric ones. (Had to change the t-nuts as well.)
I'm using six 9mm paper clips (the original ones are 7mm).