There are quite a few ...
My favourite 2 are:
Supper's Ready and Carpet Crawlers 
Uncertain weather ... ?
If something like Silver Rainbow is included it's a bit of a grey area. Would Musical Box count, is the guitar segment before "Play me..." an intro in its own right?
Other than those already mentioned - I'm not sure how many qualify:
Harlequin begins with all instrumentation and vocal immediately.
Seven Stones has the keyboard intro with vocal.
Harold The Barrel has the vocal come in straight away after the cymbal intro.
More Fool Me has the 'aaah-aaaah, naaah-naaah' etc over the initial 12-string strumming.
Broadway Melody (in my view anyway) starts right away on "Echoes..."
Cage has vocal in the eerie intro section
Grand Parade, vocal entry after 2-note prelude.
NYC, first line sung over initial bass 'pulse'
Lilith, vocal just behind 5-note entry
Anyway, first line over end of piano intro
Lamia, vocal entry straight after first opening piano phrase and continues over.
Ripples, immediate vocal over 12-string intro
Undertow, immediate vocal
Guide Vocal, immediate vocal
Please Don't Ask - hmmm... opening piano phrase then continues under vocal - ?
M&SJ - vocal enters over intro section
None on Shapes/IT I think. I've run out of steam there.
Backdrifter's post got me thinking of the original intent of the OP. I took it to mean that the vocals come in before any instruments or at the same time as the first instrument.
So, to me a song like The Musical Box wouldn't fit. But, I can't be 100% sure how the OP meant it.
Top 3:
Back in NYC: So powerful
Pigeons: Possibly the funniest.
I Know What I Like: It's One O'Clock...
When the sour turns to sweet.
That's me.
Say it's alright Joe.
