NOTE: If any of these aren't as unknown as I think, please tell me.
Tombi/Tomba one of my favorite games in the world, unfortunately too expensive for me to buy now.
Vib Ribbon was pretty fun
Abe's Oddyssey and Abe's Exoddus were amazing and almost unheard of too.
Croc was great
Summoner was one hell of a fighting game, though I'm not sure if it was well known or not.
40 Winks wasn't a bad PS1 game.
Alfred Chicken too and Team Buddies kicked ASS.
The one game I've played that I've never seen mentioned on the internet or outside of my house, Rascal. A ps1 game. Fun little thing about a boy with a bubble gun shooting things with bubble sand whatnot.
Actually I've never heard mention of Dead Ball Zone on the 'net either. I wonder how many times I'm going to remember something and edit this, so far twice.
Destruction Derby on PS1 was good, though not sure if it was well known. Correct me if it's not. (3rd edit)
Running Wild and Cardinal Syn. (4th edit) Ah, the joys of getting 90% of my games out of the bargain bin.
Snap, almost forgot one of my favorites. Bloody Roar.
Edit number 6, Rollcage. Memories are just flooding back to me now. (Also wipeout, but I'm not sure if that was well known back then like it is now)
I'm not counting edits now. the Gex games were fairly obscure if memory serves right, awesome too.
Rollaway, also known as Kula World
Creatures, there's another one.
Bomberman: Fantasy Race, Syphon Filter, Omega Boost, Rat Attack!
Mort the Chicken, Soccer Kid, Parappa the Rapper and a PS2 game, Portal Runner.
There are more but I can't remember their names. Not sure whether to put Lemmings here, is it well known?
Bajillionth edit: Crash Bandicoot and Spyro games, also not sure if those are obscure/virtually unheard of but I rarely see them mentioned anywhere these days.
Good Lord, I managed to forget Medievil.
Good Lord again, I forgot my favorite vampire game that no-one's ever heard of - Soul Reaver.
Overboard (or Shipwreckers)
Point Blank, Bugs Bunny: Lost in Time, Worms, Area 51 (ps1 game).
FUCKIN' MICRO MACHINES!
Whiplash too.