I have a first edition copy of the second Harry Potter book. I found it in a second hand store for £1, and while not as rare as first editions of the first book by a long way, it's still worth a couple of hundred pounds, and over a thousand if I were to go to an event and get Mrs. Rowling to sign it.

In terms of videogames... I don't know. Most of my stuff is pretty common, really. The games that tend to be most coveted are English editions of cult Japanese RPGs, and pretty much all my copies are Japanese originals, which have such big print runs in their home country that you can find most of them for pocket change in second hand stores. I guess I have a first run copy of Pier Solar, a fan-made RPG for the Mega Drive? They're individually signed and numbered, and mine is number 493/800 of the Japanese edition, meaning there are 799 out there just like mine, and another 1600 from the same run, but with different box / cartridge art. It's not sealed, though, as I've never really been much of a collector, and just bought it to play it and support what the creators were doing.