I've bought three 19" rack enclosures from fellow cnc-enthusiast Jiri K:
My plan is to house the PSU, based on a 230 VAC to 2x30 VAC 1.8 kVA transformer, in the bottom box (I might have to extend the encolsure a little, the transformer should the same as Sauli J:s transformers, about 220x220x120mm). The middle box will have the servo amplifiers, and the top box will contain the optoisolators and some low-voltage logic. The top box connects to the m5i20 card in the computer via three 50-pin ribbon cables.
Together with Jari we made some panels for the servo box (bottom), and the logic box (top). The servo amps connect to the motors through the round black 7-pin connectors. Each pin is rated for 7.5 A, so I might use two pins per pole just to be safe. The logic box has six D25 connectors: four for encoders (X, Y, Z, and Spindle), one for the jog pendant, and one for limit switches (we'll have to make a separate Y-cable or something for those). There's an E-stop switch to the right, and a connector+switch for AC mains.
Here I've mounted three PWM servo amplifiers and one PWM switch from pico-systems to the back of the servo box. Secured to the back rails of the box by four M3 screws to the heatsink. The 120x120 mm fan is probably a bit overkill - but overkill is fine when it comes to cooling. At the top you see the back of the motor connectors.