Hm, hard to agree with a lot of these being "little-known", but...
I nominate the following. Despite being compiled/edited by a dingus, it has a lot of interesting material from some very good players indeed (it's also where I first came across that unbelievable Kavalek B vs 2 R's game):
I also found this quite good (way back when):
This book has given me years of pleasure, also only in descriptive afaik.