POP 9

The POP 9 card set was given out for prizes for Pokemon leagues in March 2009 through September 2009 but they can still be found at some leagues and in some blister packs and other card boxes and tins. This set is fun because all the cards work together, for example one of the buizel card's attack is Super Fast which says
If you have Pachirisu in play, flip a coin. If heads, prevent all effects of an attack, including damage, done to Buizel during your opponent's next turn.
See If you have Pachirisu in play so then one of the Pachirisu card's card attacks is Poison Berry-
If you have Croagunk in play, this attack does 20 damage plus 20 more damage and the Defending Pokémon is now Poisoned.
Most of the cards work together like this except a few which are Regigigas, Manaphy, Garchomp, Gabite, And Gible. Its a fun premise and very creative.
Here is a list of all the cards from POP 9.
No.
1 Garchomp
2 Manaphy
3 Raichu
4 Regigigas
5 Rotom
6 Buizel
7 Croagunk
8 Gabite
9 Lopunny
10 Pachirisu
11 Pichu
12 Buneary
13 Chimchar
14 Gible
15 Pikachu
16 Piplup
17 Turtwig