Virtually any instrument works for looping and there are some incredible musicians out there using only their voice to create full arrangements. One of my favorites is Dub FX from Australia.
There seems to be no end to what’s possible just using the human voice and a few pieces of gear. There’s also a viral video of a girl singing Michael Jackson’s “PYT” using the same concept- although I believe some elements are prerecorded.
Percussion in looping is universal in any genre and if you’re on a big stage or in a standing room situation it’s essential. Common ways to create percussion loops include beatboxing, beating on acoustic guitars to get a Cajon-like sound, and small high quality drum machines (which are becoming standard for the modern looper). A background in percussion will come in handy for anyone wanting to loop, and understanding rhythms and drumming styles are key in creating good grooves.
Along with the voice, acoustic guitar is probably the most commonly looped instrument and looping is a perfect way for lead players to showcase their skills using themselves as rhythm tracks. This is one of the most basic and useful applications for looping and I’d encourage any guitar player interested in lead playing to experiment with it.
Digital pianos, bass guitars and synths are all viable options for instrumentation and my friend Jeremy Mangrum in BigForestFire uses a trumpet frequently in his looping. I’ve seen Keller Williams loop using household items and children’s toys to great effect. The truth is anything that is a sound source can be looped either direct or through a mic- and the more creative you can be, the more the audience will enjoy what you’re doing.