Laura Nyro and of Montreal come to mind, and to an extent, Chicago, Rundgren/Nazz, XTC, Rufus Wainwright. Zappa's an obvious one but I think we can all agree you can't put any label on his music. In the hip-hop there's Madvillain/MF Doom.

[Wozzeck]

I love the orchestral music of many operas but I'm not too keen on most of the singing. Not keen at all actually. Some of the Russian stuff is okay, I suppose----if it's sung by Russians.

The one opera that has my 100% approval is Alban Berg's 20th-century masterpiece Wozzeck----I even forked out for the full score----although it's a million miles away from Puccini and even Britten.  But the plot's just as lurid. 

Keen on sprechstimme then?  Great opera, Lulu as well. If you want to try something further out, I'd recommend "Die Teufel von Loudon" by Penderecki.

How about this one from Roy Wood; a spot on Carl vocal imitation and some direct musical quotation (I Get Around, Help Me Rhonda)
http://www.youtube.com/watch?v=VZSBTMBoLhI

"Why Does A Pretty Girl Sing These Sad Songs" is another great homage as well
http://www.youtube.com/watch?v=l9To94tvjrA

Zappa's 200 Motels, Herrmann's Psycho. I recently heard some of the soundtrack to this film noir called "Dementia", by the iconoclast American composer George Antheil, and was floored (although he outright stole sections from Rite Of Spring!)

The first 5 Laura Nyro albums. So so so so good.

Damn right they are! I've always maintained that she, alongside Brian, is one of the true geniuses to have emerged out of the pop mold. Totally idiosyncratic, ecstatic, profound music, such incredible breadth of expression. Gonna put on Eli right now.

When I first heard Lovin' Spoonful's rendition of "You Baby" (not penned by Sebastian, but Barry/Greenwich/Spector!), I immediately noticed an uncanny resemblance to God Only Knows in their respective verses (immediate beginnings of). Very similar, the melody in particular but also the rhyme ("You know I've been wanting you...). Perhaps enough to get Brian and Tony going? Seeing as the Spoonful's debut LP containing the song came out in November, and its follow up in March (the same month GOK was recorded), it's plausible "You Baby" could be the song Brian has referred to. Then again, you'd think Brian would have known it wasn't penned by Sebastian, given the actual authors, and should have known the Ronettes/Spector '64 recording if he were the fan he makes himself out to be! 

Just speculation...