Probably the best known 747 Classics are the two in the USAF Air Force One fleet, which were some of the last to be built, and actually got delivered after the -400 was in production.
It will be a moot point if I say that Virgin Atlantic are still operating them, but their Manchester to Orlando service has a Classic operated by Air Atlanta for them in Virgin livery. Also European Aviation have a number used on a range of charters - there always seems to be one on the ground at Manchester whenever I drop in there.
Many of the major operators had two bites at the Classics, the original models built in the early 1970s (which have all gone) and then replacing them in the mid 1980s with much more capable and updated versions.