The Pokémon TCG Online is a virtual version of the card game in which you can play against AI opponents and real people over the net. The best part? You can unlock more cards the more you play and expand your collection for free, or you can buy real cards and use the packed-in codes to unlock them in the game! The rules aren't too complex and the game takes care of most of it for you; automatically drawing cards, flipping coins, etc. If you like Pokémon and especially if you like the video games, you'll probably have a blast with this too. You can create an account and download the game client here.
PTCGO Info Pokémon Trading Card Game Online Leaderboard