I also stumbled upon some error cards from the Base Set, Jungle and Team Rocket releases.
Most of these cards aren't in great shape, but I'm holding on to them for their uniqueness.
Vulpix: A number of these cards have their HP's listed as "HP ##" instead of "## HP".
This must be a dime-a-dozen error since I had about ten of these.
Select Jungle cards: In an early print run of the Jungle set, a number of holographic cards were printed without the Jungle Symbol.
Rapidash and Seaking: Seaking and Rapidash are Stage 1 Pokémon but the text tells the person playing the cards to "put XXX on the Stage 1 card".
Dark Arbok: Dark Arbok was first printed with extra zeros and the number three was accidentally entered so it was written as "©1999-23000 Wizards".
Dark Golbat (holo and non-holo): The English Pokémon Power mentions "Apply Weakness and Resistance", while in the Master Rules Document, the Japanese Dark Golbat's Pokémon Power says "Don't apply Weakness and Resistance." There is also a lacking space between the words "Pokémon" and "Apply". (Reads "Pokémon.Apply")
Non-Holo Dark Vileplume: Non-holo Dark Vileplume have a weakness to Fighting instead of Fire.
Dark Rapidash: Dark Rapidash's stats lacks the word "Length".
Grimer: English Team Rocket's Grimer's Poison Gas attack puts Pokémon to sleep, although the Japanese version Poisons them.
I also have some Series 1 Topps error cards! All these cards in question have a black Topps logo, but the foil on them is smooth. Thing is, all the Series 1 cards with black Topps logos should be embossed, so these are boo-boos.
Do you have any error cards? I'd love to see pictures of other cards with mistakes on them. :)
Source for error card descriptions: Bulbapedia