Options for external "boxes" (like tivo) with wall mounted tv
There are systems that mount various devices on the back of the TV either directly attached or by using the VESA plate. Some are device specific (eg. to support Apple Mac Mini) and some generic. Depending on what you need to support, you can also DIY the plate, they're not that hard to make.

Alternatively you could run a long HDMI cable to wherever (in/through the wall and use a combination of remote control, HDMI switches etc) but that will be a lot more expensive and cumbersome to use. If you already have the wires, IR/RF remotes will usually work anywhere in the same room as long as the receivers are 'visible'. You can also use IR extenders.