In Kanto, it's Pidgeot and Raichu
In Johto, it's Ampharos
In Hoenn, it's Swellow and Manectric
In Sinnoh, it's Staraptor and Luxray.
In Unova, I don't have one yet. I don't like Unfezant as much as I like the other regions' basic bird Pokemon, and Zebstrika is black - I can't fall in love with a black Electric Pokemon... I like my Electric Pokemon to be yellow, at least partly.