Still the ultimate "WTF is that?" moment in pop arrangement history for me. I can remember being on a caravan site in Anglesey, aged 9, listening to Radio Caroline, when it came on. No guitars, no bass, no drums -- no Beatles, basically -- just Paul and a string octet. Instrumentation, no matter how unusual, has never managed to have anything like the same shock effect since.

Am I right in thinking that AC/DC had bagpipes on some of their early tracks?

I believe they used a hoover on their A Trip to Marineville album. Is that an instrument? Well it was for them I guess.

....for Riders on the Storm.
And what was that twirly thing, as played on Urnban spaceman by their saxplayer?

There's a fantastic clarinet solo on "Jerusalem tomorrow" by Emmylou Harris, notable also because the songbird actually talks it rather than singing. The clarinet solo itself is wonderful - the exception to Duke Elllington's comment that the clarinet is the ill woodwind that no man blows any good...

Oh, and "Slippin' and slidin'" by Johnny Winter features a fine rock 'n' roll harpsichord solo by brother Edgar!

In My Life - Beatles played by George Martin I think. Was a harpsichord wasn't it?

John Tams - Yonder from the Home album

the mighty crematorium organ

There was a time in the 80's when the inclusion of a saxophone signified 'class'. Now it just sounds crap.

Caravan (band of the elsewhere maligned Pye Hastings) used hedge clippers to percussive effect on the track Hello Hello on the If I Could Do It All Over Again... album

Os Mutantes used an aerosol spray to replicate the sound of a hi-hat on their cover of Francoise Hardy's Le Premier Bonheur du Jour.

Forget those saxophones and trumpets - too damned modern. If memory serves, it was Richard Thompson's album Across A Crowded Room whose "horn section" consisted of the crumhorn and the shawm. Yet another reason to love and admire the man

Played by Eric Stewart on 10cc's 'Iceberg' on 'How Dare You?'.

Presumably Wrangler zips just didn't have the right 'timbre'.

Or it was a very early example of product placement.

We used a Henry hoover for the intro to Back In The USSR. True to form, our designated vacuum wrangler had to get a girl to show him where the 'on' switch was.

Ocarina in The Troggs' Wild Thing
Theremin in Good Vibrations
Stylophone in Space Oddity

All a bit obvious, perhaps...

Are these cuicas on Smoke City's deliriously lovely Underwater Love?

The only other place I've heard them is on Jerry Goldsmith's Planet of the Apes soundtrack

"Fanfare" by Eric Matthews has a fantastic horn hook - think it's French horn, though there may be some trumpet on there too. In fact the whole album "It's Heavy in Here" is chock full of them...

Paul McCartney crunching on carrots on the Beach Boys "Vegetables". He says he can't remember it, but Brian Wilson swears it's true.

wasn't that featured on Handbags and Gladrags by Rod or so I heard?

(Sorry)
At last an instrument. Grateful as I am for carrots, aerosols and zips, I was really loking for unexpected conventional instrumentation.
And I have another example, heard for the first time yesterday. There is a group called Cake, about whom I know nothing (but one of youse will)who produce an interesting bass driven noise, with semi spoken vocals and dancey(?) guitar. And fabulous and unexpected trumpet, that most awful and maligned of the brass section. Never since Chumbawamba have I heard such gloriously positioned trumpeting. So out of place, so wrong it works like o'blimey. So bad it is magnificent.
Go hunt!
(Especially a cracking version of I will survive, where the trumpet reconstructs the remembered original after the rest of the song takes it away in advance)