To those of you who collecting all kinds of rare Mega Man/Rockman merchandise, it doesn't get much more rare than this. Check out this auction for an original Plug-In PET, which comes complete with all accessories. Current price is at a hefty $250 ("buy it now"), however, the seller is willing to negotiate via the "make an offer option." Shipping is, thankfully, free.
The original Plug-In PET toys are pretty hard to come by these days, complete sets especially. The Plug-In PET boasts a lot of neat little features and gimmicks, all summed up quiet nicely in this video review by reader Amir. I highly advise checking it out if you'd like to know more about the device... or just want to see it in action.
Part one of the review is here, part two here.