Wow! This thread is going to become my new definition of the term "nostalgia." I find it incredible that people can view the old Fiend Folio as anything other than terrible.
I used to like you.
Yes, it is true that the book gave us the Githyanki and Githzerai. However, the Drow, Kuo Toa, Jermelaine, Nycadaemon, Mezzodaemon and most of the decent monsters were just reprints of monsters TSR had published elsewhere.... For me, the emblematic creature for the FF was the Denzelian: Move: 0', Attacks: 0, Special Attacks: none. What does it do? Does it talk? No. It just sits there and eats rock. Hurray!
D00d, seriously, the good stuff in the FF includes the algoid, the al-mi'raj, the stunjelly, the slaadi, the githyanki and githzerai, the phantom stalker, nilbog, sussurus, flail snail, screaming devilkin, Styx devil, flumph, meazel, dire corbies, volt, vortex, acherai, witherstench, skulk, adherer, aaracockra, rothe, forlarren, envelopers, aleax... the list goes on and on.
I have to differ with you on the sheet phantom and ghoul, too- yeah, they're weird, but they're COOL weird.
On the other hand, the denzelian is a loser, and so are the protein polymorph and snyad. There were other offenders, too- ironically, even some of the WORST made it into 3e (denzelian is clearly the origin of the delver; what a stupid monster to update!).
But really, the FF was my favorite 1e monster book.