Acapellas

The Pentatonix are quite good imo.

Varsity Vocals puts out a compilation of collegiate a cappella every year (since the late 90s). Not all bangers, but there's definitely some good stuff on lots of the albums. I find it fun to load the whole backlog of songs up in a random playlist and then try to guess what decade the songs were performed as they play. A lot of the older stuff is more focused on harmonies and sometimes have an almost barber-shop quality to them, and then as you move forward in time you get more stuff like beat boxing, weird sound effects, and obviously distorted vocals, until the present stuff which is sometimes indistinguishable from a normal instrumental track.

Smooth McGroove is the gold standard for Acapella YouTubers who cover video game soundtracks. He's mostly retired, but his archive is the stuff of legends.

Have you heard Caroline Shaw's Partita for 8 Singers?

If you like watching talented vocalists harmonize with themselves on YouTube, lately I've really been enjoying Julia Westlin and Geoff Castellucci.

I'm fond of the Newfangled Four. I'm not sure if barbershop counts for your definition of a cappella, but they're fun.

For something completely different: choral a capella

Eric Whitacre's Sleep, performed by BYU, is one of my all time favorites.

Well, since you said anything, definitely check out Todd Rundgren's 1985 album A Cappella. It may not be quite what you had in mind, but it's a pretty interesting creation, especially for its time. The only source of sound on the album is Todd's voice, but you don't necessarily realise it unless someone points it out.

Songs like Lost Horizon and Something To Fall Back On sound like pretty conventional pop tunes. Others like Miracle in the Bazaar don't. But the point is, there are no drums. Just Todd's voice. No synths. Just Todd's voice. No bass. Just Todd's voice. And so on.

The trick is that Todd sampled and manipulated his voice in various ways to make it sound like conventional instruments. Which was quite a feat in the mid-80s. But why, you might ask, would anyone go through all that trouble if they wanted the end result to sound close to more conventional instruments. Well, because it's Todd. Todd has the habit of taking a concept to its breaking point, and then laughing as he pushes it further. Much further.

That said, the album also contains songs that are a little more like traditional sounding a cappella songs, like Johnee Jingo and Pretending to Care.

If this concept intrigues you, there was actually a pretty nice interview with Todd about this a few months ago. You can see it here. He talks about his motivations and the process of making the album.

Solo is one of the best examples of Prince's vocal range and skills. I really love that song. It includes some sparse accompaniment, but it's really all about his voice.

Honestly can't stand most a cappella music (at least in the current popular understanding of the term). If a song is going to be all vocals, I'd rather have a good choir arrangement. In most cases a capella songs are just pop songs with someone doing decent beatboxing and someone who can hit the low notes making belching sounds, which isn't anywhere nearly as appealing as if they used either real instruments or at least a decent synthesizer. Because they are almost always using the same vocal techniques for every song, each a cappella group sounds like every song they play is the exact same song.

There is one a cappella song that I like which a lot of people these days don't like, and it just happens to be the first a cappella song to reach #1 in sales - Bobby Mcferrin's Don't Worry, Be Happy. And to be honest the big reason why I enjoy it is because it's performed and produced well enough that it really doesn't sound like a capella.

(Also the music video fills me with a very pure and slightly nostalgic sense of joy and happiness because it's got a young Robbin Williams in it.)