Skylanders figures are now the rarest available.
Activision hired a PR company prior to E3 2011 to build excitement for Skylanders. The PR company mailed 1 of 3 figures to various gaming sites and news publications. The figures were either Spyro, Gill Grunt, or Trigger Happy. Each one had a sticker on the front that looked like this:
According to one of the journalists who received a figure and sold it on eBay, Activision probably made about 600 of these figures for distribution before and during E3.
If the number of copies is split evenly among the three versions there are only 200 of each figure.
Only the figures still in the original box are rare because the figures are identical to the standard Series 1 figures. Once the package is open they become indistinguishable from figures that sell for $4-5 each.
The purpose of the promotion was to open the figures and use them on the game at Activision's E3 booth. Because of this many of these were opened.
Nobody knows the exact number of sealed copies available for these rare figures, but it is probably close to 100-150.
Only two of these have come up for auction that I am aware of, both Trigger Happy. One closed at $62 last March and another sold for $503 with a Chrome Spyro from E3 2012.
Hopefully more of these E3 2011 Skylanders come-up for sale soon so we can know the actual value. My guess is they will be the most expensive Skylanders figures ever sold when they do sell again.
Thanks to DluA on DarkSpyro forums for much of this information on the 2011 E3 variants.
E3 2011 Model Number Image