Not sure what counts as obscure...games nobody seems to own but may have heard of, or games no one has heard of?
Probably my least commonly encountered games are Delta Force (Task Force Games), The Price of Freedom (WEG), Man Myth & Magic (Yaquinto), and Crime Fighter (Task Force).
I've never even seen another copy of Crime Fighter, which surprises me because Aaron Allston is well known and well respected. I would have thought his name on the box would've sold more copies.
Have quite a lot of other games where I have never met anyone else who owned them, but those are the ones from major publishers. All are bad ass in their own quirky ways.