rarest games i had (all have found good homes with 2600 collectors since) are:
- boxed video jogger/video reflex w/ mat
- complete berenstein bears
- sealed boing (my first big find, in NJ near DPHQ believe it or not :)
and then boxed versions of: silver gravitar, condor attack, spider fighter, bumper bash (which don't really count as i am in canada and have found multiple copies of all of them -- including 8 bumperbashes over the years)

rarest game i have, and will have for the rest of time:
mr boston (complete) - vectrex

other rare stuff:
minetstorm 2 (loose) - vectrex
tomarc/motocross racer (boxed) - colecovision

rare homebrews i was lucky enough to snag:
kevtris - colecovision
ms. space fury - colecovision
okie dokie - 2600