I don’t know if this is what you are looking for, but on the 25th (30th?) Anniversary release of George Harrison’s “All Things Must Pass”, one of the bonus tracks is an instrumental version of “What Is Life”. It basically sounds just like the original version, only with the vocal tracks removed.
They’re too far out of the mainstream to belong on your mix, but in the years around 1930, several record companies used to get the big dance bands to do what us 78 nuts call “non-vocals.” These were the same arrangement as recorded for domestic 78s, just without singing.
They were typically meant for release in non-English-speaking countries, or for PA system use in theaters. Some of them have interesting jazz solo work; they’re all fun to have, but of course, only if you’re into this stuff.
Rick Wakeman recorded a version of Summertime that is worth a listen.
Stanley Jordan’s solo guitar version of Eleanor Rigby is one of the most incredible pieces of music I’ve ever heard. The versions available on YouTube are not as good as the original album version (‘Magic Touch’) but give you a taste of the man’s incredible technique. And his version of Autumn Leaves is worth a listen.
That reminds me, didn’t Kronos Quartet do a version of “Purple Haze”?
A friend of mine back in college had an album by some group called “The Temple City Kazoo Orchestra” with kazoo versions of the theme from 2001 (which was actually quite good), “Whole Lotta Love”, and “Stayin Alive”.
It was originally an instrumental composition; the lyrics were added later. (When I looked it up on Wikipedia to confirm this, I discovered the most unintentionally goofy opening sentence to a Wikipedia article ever)
The Kinks recorded an instrumental version of “Lola” (for their “Percy” soundtrack album), though it’s nothing special.
And then there’s Thrillington, which, to my pleasant surprise, I got as a bonus disc with my copy of McCartney’s Ram.
I’d bet dollars to doughnuts this is only available on vinyl (and of course long out of print) but at a Beatles convention I picked up this fantastic album called something like “The George Martin Orchestra performs the music of Help!” Which was the entire soundtrack (and I think some of the incidental music) done in Mantovani-style instrumentals.
Rhino Records also has some stuff in their “Ultra Lounge” line you might want to check out. (“On the Rocks Pt 1 & 2” are especially good.) It’s mostly easy-listening and jazz stuff with a bunch of it cheezy breath-y singers doing pop and hard-rock from the 60’s & 70’s but there are quite a few instrumentals as well. You can listen to samples at Amazon (and I think buy individual tracks.)