moving overseas led me to look at everything I own based upon it's weight and volume vs. perceived value. many comics, along with half of my record collection, didn't make the cut, and instead were donated to friends in Texas.
I'd love to see my Groo the Wanderers back again someday, but I'm not holding my breath.
to answer the topic, I'd say, the Bill Sienkiewic epic Stray Toasters, followed by anything else Bill S. drew the cover for, and then Alan Moore's Neonomicon stuff.
really, when you're put to the task, everything is expendable.
currently, I live for the series "Low" on Image Comics. I'll be making a pilgrimage to the comic shop this weekend to pick up the last one (#6) that came out this week. the compendium is due out soon; do yourself a favor and be the first in line to get it.