Sabatia dodecandra, Large Marsh Pink
Flowers have 8 - 12 petals.  The others usually have five.

Sabatia difformis, Two-formed Pink
White flowers.

Sabatia angularis, Square-stemmed Rose Pink
Stems are "distinctly 4-angled or ridged".  (Sabatia difformis also has square stems.)  Not rare, and it's the only Sabatia species found in the Piedmont.

Sabatia campanulata, Slender Marsh Pink
Leaves are rounded at the base, with obtuse tips.

Sabatia stellaris, Sea Pink
Leaves are tapered at the base, with acute tips.  Not rare.

Sources: The Flora of Delaware, Herbaceous Plants of Maryland.