Ok, so i found this link on Dakka, and it's excellent!
Collecting Citadel Miniatures Wiki.
It basically has an archive of unreleased and limited release minis, which i've certainly never heard of - and i thought i knew a lot about this hobby.
Everyone knows about the 'adult' witch elves and Vect's slaves, but did you know that GW made a Halfling pimp? Or that they originally designed Cypher with a face mask (which looks far superior to the current Cypher).
How's about a range of Cadian officers and tank crews that were never released? And my favourite: Did you know they designed an entire range of TK tomb guard that all had to be scrapped because they looked too much like the guard in The Mummy Returns?
An excellent website, although they are missing quite a few bits. Check it out if you get chance!