The first one with all the Russound audio gear is a Middle Atlantic SRSR that pulls out and rotates:




The dual side-by side racks are from SnapAV, but I also use the Middle Atlantic CFR series which are the same thing but not as deep.  These racks simply sit in the base cabinet and have plastic runnners on the bottom so you just slide them out and place on the floor. 

This style came out a couple years ago from MA and I use them all the time now.  Better access than the slide out and rotating style and they cost less.  They only go up to about 16U in height so they aren't that heavy and you can easily pull them out as long as you have good cable management.

If you noticed in the photos of the side-by-side setup the outlets and cable bundle are up high in the cabinet which makes a nice service loop.  If all your cables come out in the bottom of the rack, it will be hard to push the rack back in without bunching up all the wiring behind it.

Here you can see the rack pulled out of the cabinet.  Easy access to the back.