Mexico could have split three or more ways at various points in history - ending up with Yucatan, Mexico (the core plateau region), and Aztlan or the Rio Grande Federation up along the US/Texas (dep on TL) border.
Argentina, as noted, could have split with a BA centered city-statelet, and the rest as a separate entity.
Brazil was sufficiently large that you could have the south costal highlands as one entity (prosaicly name Brazil, as that's where most of the population & wealth are), and the river basin to the north under a different name/ownership - possibly Amazonia? <ducks>.
Bolivia and Paraguay could both have split, given their poverty and the various coups/countercoups.
In a cartelwank tl, Medellin and parts of the country side could split from Colombia proper - possibly under the cover of a leftwing/rightwing civil war.
Under the same approach - you could have an East/West Cuba, if castro had made the mistake of making his anti-americanism and communist leaning more obvious/offensive to his northern neighbors before consolidating his position.
As a last casualty of the cold war, there was a portion of eastern Nicaragua that was the base of support for the contras - that could potentially have hived off and formed a new US sponsored statelet under the right conditions.
Venezuela could even have split apart, in a TL where their conflict with the UK went hot, with a UK hostile state to the west and a UK friendly state to the east (or south/north).
Or, you could go farther back, and change the settlement patterns - if a whole slew of nations start colonies at various points - that would seem to lead to more possibilities for greater balkanization.