While guitar straps may not be the most “exciting” guitar accessory on the market, they’re easily one of the most useful. A good strap not only makes playing the instrument standing up possible, it can actually make the guitar easier to play, which is why many players (myself included) still use a guitar strap even while sitting down.
As with most types of gear accessories, there are many different choices regarding the style, material, and design. Let’s start with the design first. Due to the ease of customizing and even creating different designs, it’s safe to say that if you can dream of a particular strap design, chances are there’s someone who will make it for you. Still, most players tend to opt for single colors, and companies like D’Addario and Ernie Ball make inexpensive nylon guitar straps that are available in a wide range of colors. Some artists (like Joe Satriani) even make their own strap designs with a variety of colors and artwork.
Of course, there are guitarists who tend to favor more traditional materials and looks, and there are many different kinds of leather and suede straps for these players. These straps are often padded which can make holding a guitar such as a Les Paul for a couple of hours much easier on one’s back and shoulders. My personal favorite strap is made by Neotech, and it's incredibly comfortable, even when playing a heavy guitar such as a Les Paul.
Unless you just like taking chances, you’ll probably want to find a way to secure your straps to your guitar. Devices known as “strap locks” are the most common choice, with models by Dunlop and Schaller being the most popular. Honestly, there are good reasons to choose both, and I’ve used both Dunlops and Schallers with great success in the past. Personally, I prefer Schaller Strap Loks just because I prefer the way they attach to the guitar and I personally think they look more aesthetically pleasing than the Dunlop locks, but that’s just a personal preference.
Another common choice is to use washers from Grolsch beer, which allows you to keep your stock strap buttons (especially on vintage or vintage style instruments) and still secure the strap to your guitar. Fender makes a Grolsch-type rubber washer that is perhaps easier to find than a used Grolsch beer bottle.
Finally, you can even buy straps today that have a locking mechanism built-in to the strap. The most common version is the Dimarzio system where the straps are secured by a locking plastic mechanism that - I must admit - if installed properly is likely the most secure locking system available today, though I personally don’t care for the system since you have to keep part of the strap installed on your guitar at all times.