Two Lego Mindstorms sets have been released prior to 2002. The first set featured R2-D2 which can also be converted into a Battle Droid on a STAP and a Treadwell droid. The second set was an AT-AT which can be converted in to a Destroyer Droid and Droid Starfighter (walking mode).
The set with R2-D2 is called the Droid Developer Kit. Released in 2000, it is numbered 9748 and contains 657 pieces.
The AT-AT set is called Dark Side Developer Kit. Released later in 2000, its number is 9754 and it contains 578 pieces.
Keychains/keyrings are very popular Lego sets. Until recently, only single characters were released as keychains.