Putting together a good guitar rack system takes time as you will need to go through the various components available to you. As your style and tastes change through the years, so may your choices when considering the many different types of component. The heart of a good rack system is not only the quality of components you choose, but also the quality of wiring you use to hook them all together, so consider spending quite a bit of money on cabling for your rack mount system.
Construct your guitar rack system around a rack-mountable amplifier. Mesa Boogie and Marshall both make rack-mountable guitar preamp/power amp heads. They come in a variety of configurations from all-tube to solid state and vary in price from a few hundred dollars to thousands of dollars for custom, handmade models. If no all-in-one head is suitable for you, you can get a preamp/power amp combo and mix and match the various brands.
Add a rack-mountable tuner in order to stay in tune during practice and at shows. Staying in tune is one of the most important, often-overlooked aspects of a guitar player's gear. Korg, Peterson and Behringer all make rack-mountable tuners that are very accurate. Peterson has a strobe tuner available in rack mount form that is used by industry professionals and recording studios around the world.
Install a wireless system in your rack. Shure, AKG and Line 6 all make digital wireless systems that can be placed in a rack. These digital systems are capable of reproducing a full range of sound covering all of the frequencies and can sound as good as a guitar plugged into an amp.
Include a power conditioner in your rack to make sure that all of the units get the proper electrical current. These rack mounted units need stable power to run properly, especially amp heads as the tubes need stability to sound at their best. Power conditioners are similar to power strips, but they also regulate the voltage of the power coming in to curb spikes and dips.
Add a multi-effects unit to complete your rack mount system. Multi-effects units can provide you with user-tweakable effects such as reverb, delay, compressor, flanger and often have built-in simulators of popular amp sounds. This can allow you to play different styles and does not relegate you to the sound produced by your amp. Many multi-effects units also have built-in tuners.