Rojo congo - deep color, can really grow to be a real beast with thick stems and big leaves
Black cardinal - even darker, glossy leaves
Billietiae - can be expensive, but the stem color, leaf shape and texture is super cool. Philodendrons atabapoense and 69686 are two others along the same vein; expensive, but unique leaf shapes
Brasil - can be hung and treated similarly to a pothos if you want a companion for it. Philodendron neon is another one that is nice hanging and the color is really bright!