Platinum & Gold UPC variants
Marvel Comics, August 1990.
The 1990's was an age of speculation, with publishers printing multiple variants and using marketing gimmicks such as ashcans, sketch covers and embossed covers (some have even called the decade the Chromium Age).At the top of the speculation pile, at the start of the decade, was Spider-Man with seriously gigantic sales of over 2 million copies for the #1 "Collections Item".
With the enormous sales of this issue, Marvel decided to reward retailers with a "Platinum" variant and chose a thicker cover for that "quality" feel; ironically, the paper stock did not work well with the printing process giving rise to multiple problems, including color breakage all down the spine. To the right is the top left corner of a CGC 9.8, which is still the top grade despite over 1100 gradings (all the other variants have higher grades).
The estimated print run for the Platinum variant is around 10,000, with 7,000 given as gifts to retailers for making Spider-Man #1 "the most successful comic in history" and these were accompanied by a letter of thanks from Marvel (shown below); the other 3,000 were apparently sold off in bulk later.
There are always plenty of Platinum variants for sale and sometimes even the letters themselves are for sale separately; a CGC 9.8 Platinum would set you back $575 in July 2014.
The Gold UPC variant or Wal-mart variant is thought to be rarer than the Platinum but also sought after in high grade (but not quite at the same price level as the platinum). A CGC 9.8 Gold UPC variant would set you back around $450 in July 2014.
Below is the cover art that sold by auction for over $350,000 in 2012: