For me, the epics have to be the Martini and Castrol liveries. They are by far the most distinctive of all liveries, ever. Close followers are the Lancia/Alitalia and the silver Audi with red rings.
Other epics of note are the Renault 2006 and the old Rothmans, the JPS and the latter-day McLaren Vodaphone.
Epic fail must go to Honda's cluttered and incomprehensible "Earth" livery which, though I'm sure it looked great on paper, was shockingly attrocious on the car itself. I still have no idea how it was allowed to make it as far as the pitlane.