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I have decided to go with Base Set Gyarados, Base Set Blastoise, and Fossil Articuno. I was also thinking about adding in Rocket Dark Gyarados, but I'm not sure if it would be a good idea.
Another thing you could get is the Red Genesect Deck. It has a lot of good trainer cards, and is probably better than most theme decks. They're about $20 though.
I was building a deck to play casually with cards from the Neo sets and older. Here is the deck list
16 Pokemon
3x Totodile neo genesis
1x Croconaw neo genesis
3x Feraligatr neo genesis #5
2x Squirtle base set
1x Wartortle base set
2x Blastoise base set
4x Cleffa neo genesis
24 Trainers
4...