Grubb's most enduring legacy is the 1987 Manual of the Planes, which expanded on E. Gary Gygax's summary in the Dungeon Masters Guide. This became the Great Wheel of Planescape. Grubb came back to deliver the excellent graphic novel in Hellbound: The Blood War.
With his spouse Kate Novak (they're still married, which is awesome) he wrote Azure Bonds whose sequel is the 1988 software game "Curse of the Azure Bonds". That game got translated BACK to paper as module FCR2.
Nowadays the man shouts at clouds over in the Grubb Street blog.