Tuning and retuning might be a drag if you use several tunings. However, there are a few options (meaning gadgets) that can help you.
For my part, I own only one of these: the Strobostomp tuner. However, I have my eyes on the Trilogy bridge for my Strat and possibly one Keith tuning peg for my Tele.
The Transperformance guitar
This is an electro-mechanical device which tunes your guitar to the tuning of your choice from an onboard database of tunings. This is absolutely the top-of-the-line, with a price to match. How do you get one? You have to send your guitar to the Transperformance company and they will hack your guitar to install the mechanism. Don’t send your ’59 Les Paul…
You might be interested to learn that Transperformance is working on an acoustic prototype.
The company behind Gibson’s so-called robot guitar. This mechanism works pretty much the same as the Transperformance guitar but modifications are less dramatic: you have to change the tuners and install a special pick-up close to the bridge. Whereas the motors of the Transperformance are at the bridge, the motors of the Tronical system are in the tuners themselves. In regards to alternate tunings, you are somewhat limited. You have a small bank of user presets (less than a dozen) from which to choose. You can, however, reprogram the presets.
The Gibson robot guitar costs several thousand dollars but Tronical markets their bare system at less than 2000 dollars.
The VG-99 and its predecessor, the VG-8 are sound modelers. The onboard computer simulates a guitar tone and, more importantly for us, virtual tunings. The guitar of your choice stays in standard tuning but the VG-99 will simulate any tuning you may wish to use. As with all computer modelling, a slight delay occurs between the strike of the strings and the sound produced. The VG-8, however, was deemed powerful enough by Joni Mitchell to bring her out of semi-retirement and go on tour again.
A special-purpose bridge (models exist for many types of guitars) that allows three presets per string. The tuning is changed mechanically (with a lever). This system can theoretically give you 729 distinct tunings. At about a couple of hundred dollars, this system is cost-effective.
These tuning pegs, designed for banjo, can also be used on guitar (as can be seen on the picture below). There are other makers of so-called detuners but Keith was the first one to make them and they are highly regarded. These pegs have only two presets each (normal position and detuned) and installing one on each post will cost you a lot more than a Trilogy bridge. However, if you only need to detune for specific strings, this is the option for you. These pegs can be bought directly from the Beacon Banjo company, which manufactures them.
Last but not least, you need a good ear. However, a tuner has never hurt anyone and the Strobostomp is the best bet you can make short of buying more expensive gear from Peterson. The Strobostomp has many presets that allow you to intonate the guitar to your liking.
The Strobostomp will also help you tune the guitar more precisely than all the usual guitar tuners on the market.