A year ago, I made a post about all the novels I've finished. It's got everything except POSSESSING LUCY (YA paranormal suspense, currently at fourth-draft stage, theoretically the first in a quartet) and THE HALFWAY HERO (YA high fantasy set in a Mesopotamian/Egyptian-esque world, currently partway through the second draft--on hold while I do my GutG revisions--possibly the first in a trilogy).
Which is a lot in itself. (I had a very long learning curve. The fact that I started when I was 13 probably didn't help.) But that's just the novels I finished! There were many many more, mostly in my teens, before I learned that, yes, I really did need to outline if I expected to get to the end of a novel. I have a whole folder dedicated to "Not Finished Stuff". Most of them I only got a couple chapters into before realizing it wasn't quite working.
The ones that got the furthest:
GRYFFON CHILD - 1995 - Adult high fantasy - Made it to 30,000 words - Stopped because I'd written myself in to a very cramped corner, I had no idea where to go from there, and I'd lost interest in the story.
ODYSSEY - 1995 - Adult, somewhere between fantasy and science fiction (kind of like the Pern series, where there's some connection to Earth and some tech but mostly it's fantasy-ish) - Made it to 42,000 words - Stopped because I had no idea where the story should go and I'd run out of inspiration.
SILVERSELF - 1996 - YA science fiction - Made it to 35,000 words - Stopped because I'd stopped feeling connected to the characters and I didn't have a strong enough sense of where the story needed to go next (sensing a pattern here? ;) ).
CHLOE - 1996 - YA science fiction - Made it to 10,000 words - Stopped because I didn't know where to go next with the story.
STARS FALLING - 1997 - YA mainstream with a little magic realism - Made it to (this pains me) 73,000 words. Which, yeah, is longer than any of my finished novels. And it wasn't close to done. :P - Stopped because I realized I was rambling on and on and the story didn't ever seem to end, and I was getting sick of it. It really was an epic (spanning several years of the MC's life, from grade six to high school).
Untitled kidnapping story - 1998 - YA mainstream - Made it to 10,000 words - Stopped because I didn't know where to go next.
I think that the last novel I wrote, and made it any distance into without finishing simply because I didn't know how to continue. I'd finally learned that lesson about outlining! I have no idea why it took me so long, considering that I had completed four novels at that point, all but the first (and worst) of which I'd done chapter-by-chapter outlines for... You'd think it'd have occurred to me sooner that there might be a connection between the outlining and the finishing. ;)
Since 1998 I've only had one other novel I made significant headway with, and then stopped--which is INNER DEMONS (YA paranormal, 28,000 words). With that one it came down to lack of pre-thinking rather than lack of outlining. I started it during the writing retreat last year when the idea wasn't fully formed, and after trying to keep it going for a couple weeks realized that I wasn't connecting enough with the characters and there was something missing. But both GIVING UP THE GHOST and THE HALFWAY HERO started as ideas I tried to write, set aside for a while and then came back to, so it may not stay unfinished.