Blue Demon -- in Jeff's original concept, created when Jeff was maybe 11, the last Brother of the Atom was named Man o'War, and he was basically Reed Richards wearing a helmet that looked like a sputnik. Jeff later realized he couldn't use such a derivative character in a team that already had so many resemblances to Marvel's Fantastic Four, so the two of us designed a replacement for Man o'War named Blue Demon -- a superhumanly fast, strong, agile hand to hand fighter. Along with his brothers Bronto and Megavolt, he fills out a pretty well designed three person team of balance.
A never used cover for Jeff's webzine, Major Attitude Adjustment's War Journal. I published this posthumously for Jeff in the Amateur Press Alliance that he and I were both members of, LEGENDS.
Baron Bunny, an evil funny animal from one of Jeff's RPGs.
The Blue Bat, another superhero from that RPG we created for Steve Jackson Games.
Mirror's End -- much of Jeff's artwork and creative concepts were drawn from the lyrics to Blue Oyster Cult songs. Like all us BOC fans, Jeff frequently misheard their lyrics; as it turns out, the lyric Jeff thought he heard in the song "Astronomy" does not actually say "Mirror's End", but, rather, the more mundane phrase "mirrors it". However, Jeff created an entire cosmogony around the phrase Mirror's End, and later did this wonderfully evocative drawing to show what he thought "Mirror's End" would look like.