I've been trying this lately:http://www.pokemontcg.com/
There are two games in that website,
1) Pokemon Training Challenge
Basically, you play against NPC using theme decks (like structure decks in yugioh or power file in here). For starter (and free players), you got each Basic Red, Blue, and Green. There are five other theme decks that can be unlocked by inputting the code got from buying the real theme decks.
2) Pokemon TCG Online (Closed Beta)
This one is where you can build deck, play against others, and trade cards. Since it is closed beta, it is only accessible by buying at least one booster pack of BLW and input the code in that particular booster pack... at least until the end of august. After that, the game will move on to open beta, and it is still unknown if free players can access it thereafter. Only for this closed beta, players will get some free booster packs. Play longer and you'll get up to 20 booster rewards as thanks when the game open to public.
Anyway, I only tride Pokemon Training Challenge so far. I have to say it's quite good. here's my review in form of plus-minus:
(+) Fully-automated Pokemon TCG. It's quick too if you disabled the animations. Even quicker if you click the game continually.
(+) I really like the 'how-to-get-cards' system. Rather than buying separately for the offline and online version (like yugioh and its official online game), this game combines both
Oh, and you can trade.
(+) A lot of developers, so the game is continually being developed (at least for now).
(+) Seeing the forum posts, I assume the community is huge and the company moderators, which are many, are not a lost cause.
(+) Nice avatar system, but it might be not your taste.
(+) Very nice (but slow) tutorial. It helps me a lot
(-) The interface is a bit awkward I think. One most important thing I dislike about the interface is there is no big-card-details-upon-hover. You have to click the card to zoom and see the card's effect, which is rather annoying.
(-) Human POV. It made seeing your opponent's cards a chore. I prefer the bird POV like in here, current NDS Yugioh, DuelingNetwork, etc.
(-) It looks like the target gamers are far more for kiddies. i.e. what browser games nowadays include parental section? Of course it can be a plus for others :v