I'm interested in hearing about individual/sub-group writing credits from songs during the phases where group credits were routinely given i.e. PG-era and post-Abacab. Below are ones where non-group credits during these eras have been indicated either in interviews, articles/features, or what I've heard other fans say. Please feel free to correct and/or add to.
EDIT: I've tweaked it according to others' comments (see posts below) and some other info I since came across.
EDIT 2: Since DecomposingMan helpfully pointed here to the "actual credits" entries on wikipedia, I've linked to those entries for each album, see bold inserts. They're interesting reading.
Wikipedia entry for Trespass here
Wikipedia entry for NC here
For Absent Friends - Hackett/Collins
Harold the Barrel - Gabriel
Harlequin - music Rutherford, lyrics Banks
Wikipedia entry for Foxtrot here
Watcher Of The Skies - lyrics Banks/Rutherford
Can Utility - first section (and lyrics?) Hackett, remainder mainly Banks/Collins/Rutherford jam, title by PG
Horizons - Hackett (possibly the only instance of one being just blatantly obvious?!)
Supper's Ready - first two parts from pieces Banks wrote at university, Willow Farm PG, Apocalypse Banks/Collins/Rutherford jam
Wikipedia entry for SEBTP here
Moonlit Knight - Gabriel/Hackett, coda by Rutherford
IKWIL - main riff and verses Hackett, chorus Banks, lyric PG
Firth - Banks, with some lyric contributions from Rutherford
More Fool Me - Collins/Rutherford
After The Ordeal - first part Hackett, second part Rutherford, though some fans believe it's all Hackett and wikipedia entry for the album backs this up.
Cinema Show - instrumental Banks/Collins/Rutherford jam, lyrics Banks/Rutherford with 'Romeo & Juliet' suggested by PG
(The Lamb - it's well-documented PG wrote all the lyrics apart from The Light Dies Down)
Wikipedia entry here - some very interesting ones!
The Lamb - Banks/Gabriel (TB says it's the last song the two of them wrote together)
Fly On A Windshield - Banks/Collins/Hackett/Rutherford (the 'pharaohs') jam, possibly Hackett providing the bridge to Broadway Melody
In The Cage - mainly Banks
Back In NYC - mainly Rutherford
Hairless Heart - Hackett
Carpet Crawlers - PG (in a hurry for once in his career when he realised there was a gap and the others were fed up by this point), finessed by Banks
Lilywhite Lilith - Collins
Anaesthetist - Hackett
The Lamia - Banks
(it's been suggested the lyrics for the above two were substantially by the named writers)
Riding The Scree - Banks/Collins/Rutherford jam
Behind the Lines - lyrics Rutherford
Turn It On Again - lyrics Rutherford
Wikipedia entry for Abacab specifying lyricists here
Keep It Dark - at this point there were still individual credits but this song has been credited to Banks
Dodo/Lurker - as above
Wikipedia entry for Genesis specifying lyricists here
Home By The Sea - lyrics Banks
Silver Rainbow - Banks
Wikipedia entry for IT specifying lyricists here
Land of Confusion - lyrics Rutherford
Domino - lyrics Banks
The Brazilian - Banks, working from drum pattern by Collins
Wikipedia entry for WCD specifying lyricists here
Hold On My Heart - mainly Banks
Fading Lights - Banks
I think PC got more involved in the lyrics at this later stage.