You really can't miss these two: they're the sky and the earth after all. But we're happy to give you a few deets just in case. Oh, but one thing first: you won't ever get to chat with them at the same time—they're always separated by their dad, Shu.
Build: A giant male (as big as the earth, usually shown lying down). Sometimes he's crowned and seated on a throne. Rarely, Geb has a snake's head, is (completely) a snake, or is shown as a crocodile or turtle.
Complexion: Reddish-brown or black, like Egypt's soil
Hair Color: Black, if it is shown
Facial Hair: A long black beard
Scars/marks/tattoos: None; though as earth, he has plenty: valleys, trenches, rivers, volcanoes, etc.
Jewelry and accessories: A gold collar and bracelets. Sometimes he wears a goose on his head (the hieroglyph for his name) or a tall white crown with horns like his son Osiris wears. He carries a Was scepter, the jackal-headed (or Seth-animal headed) staff that is the hieroglyph for strength.
Clothing: A white linen kilt, if he wears anything (he's often shown naked)
Type of Weapon: None (unless earthquakes count)
Build: Giant female (as big as the sky, usually shown curving over the horizon with her ankles and fingertips touching the ground). Nut can also be a cow, a giant sow (a female pig), or a sycamore tree.
Complexion: In human form, Nut is deep blue and covered in golden stars or has pale yellow skin (the color used for women in ancient Egyptian paintings). Almost all images of her are naked.
Hair Color: As black as night
Facial Hair: None
Scars/marks/tattoos: Sometimes she has stars on (or in) her skin.
Jewelry and accessories: Sometimes she carries the sun (in the form of a big red ball). She can also be shown with a gold collar and bracelets or with wings like her daughters Isis and Nephthys.
Clothing: Who needs clothing when you have clouds and stars? Every once in a while, Nut wears a tight-fitting dress in red, blue, gold, or white.
Type of Weapon: None
Shu and Tefnut
The star gods
Ra and the gods on his boat