I’ll go first:
DUFF BEER
VITAMETAVEGEMIN
GUZZLER’S GIN
SPACELY SPROCKETS
COGSWELL COGS
BIG KAHUNA BURGER
Not accepted answer: LOG by SPUMCO, because Nick did actually sell a log.
The answers are pouring in. Noted scholar James G. writes:
The Simpsons has had several great fake knock-off brands:
SORNY
MAGNETBOX
PANAPHONIC
and my favorite would have to be an infringement of a product that also doesn’t exist:
FUDD BEER
Of course, these things work a little in reverse (the real DUFF).
AND MORE:
GENCO Olive Oil
WHIZZ-O Chocolate crunchy frogs
UPDATE: LJW Of NYC writes to add:
OCEAN By Calvin Klein
HENNIGAN’S Scotch
LARAMIES Cigarettes
KRUSTY KRAB KRABBY Patties
CUP O’ PIZZA
OPTIGRAB glass holders
OCEANIC Airlines
ACME exploding bird seed, exploding carrots, anvils, huge slingshots, etc.
AND WHILE WE ARE ON THE SUBJECT OF ACME:
All ACME products can be viewed here.