Check your local library for one of the more recent turtles of the world books. There's a newish edition of Ernst, Lovich, and Barbour, as well as a more conservation-focused turtles of the world book by some French authors whose names I can't recall. Either will reflect recent taxonomy, though they aren't perfectly up-to-date. There's still a lot of debate over species status of various tropical populations. The whole group ranges from the US to Argentina. Most of the diversity is in the Caribbean and Mesoamerica.
There are three species, one with three subspecies, native to the US:
Puerto Rican Slider, Trachemys stejnegeri stejnegeri: Puerto Rico
Big Bend Slider, T. gaigeae: South Texas
Yellow-bellied Slider, T. scripta scripta: southern Atlantic slope, FL to VA
Cumberland Slider, T. scripta troosti: upper Tennessee and Cumberland rivers, TN and KY
Red-eared Slider, T. scripta elegans: south central US, mainly in Gulf of Mexico drainages (widely introduced elsewhere)