I came across this thread on the Fountain Pen Network where various notebook addicts ‘fess up. No photos, unfortunately, but the collections described include these:

Rocket1:
2 Paperblanks
2 A4 Rhodias – one stapled at the side and one at the top
1 Small Rhodia- I forget which size
1 A6 Rhodia Webbie
1 A5 CF French Ruled
2 A4 CF – one french ruled and graph
3 A4 CF refill pads
2 pads of CF Triomphe

stefanv:
1 Whitelines hardbound notebook (that I actually use daily for work).
1 Whitelines staplebound cahier that is just a source of Whitelines paper for testing.
1 Moleskine pocket quad ruled book that I don’t use much because of the cr*ppy paper.
1 Clairefontaine pocket quad ruled book that I do use (and keep in my pocket).
2 Rhodia “Reverse” notebooks (they are square and can be used as sidebound or topbound), but I haven’t used them yet.
2 Clairefontaine A5 spiral bound books. I used to use these for work, but have found the (quad) ruling too dark in the newer ones.
1 Clairefontaine A4 spiral notebook.
2 Rhodia pads, one dot ruled on white paper, and one quad ruled on yellow paper.
1 Staples Sustainable Earth bagasse notebook.
Several cheap German school notebooks (with better paper in them than expensive North American notebooks).
1 Picadilly blank notebook that I haven’t used yet.

Read more at Notebook Addict! – The Fountain Pen Network. I hope other notebook-addicted FPN members will continue to add to this thread. (Even if you’re not a fountain pen user, the FPN forums are a great place to read about different notebooks and paper items too.)