Alice Perrers was quite the ambitious mistress, though we have to have some sympathy for her—she has been hated in her time and ever since.
Anne Hyde nearly became Queen of England but died before her chance to. She was a commoner who, through good luck, became the mother of Queens Mary II and Anne.
Sarah Lyttleton was a beloved mother figure to Queen Victoria's nine children, all of whom kept fond memories of her as they lived their grand futures.
Elizabeth Tailboys was a daughter of Henry VIII, but since she was illegitimate, her story isn't told much, though it seems quite fascinating.
Catherine of Aragon is famous for being the unfortunate first wife of King Henry VIII. When he was just a royal nobody, Catherine became ill with sweating sickness.
Rosamund Clifford (c. 1150 - c. 1176) was Henry II of England's mistress. Unluckily for her, his wife was Eleanor of Aquitaine, who was not at all fond of The Fair Rosamund.
Mary, Queen of Scots, is famous for being executed by her cousin, Queen Elizabeth I. Before her beheading, Mary wrote a letter to her brother-in-law, Henri III.
Berengaria of Navarre became Queen of England in the 1100s, but because her husband was always on crusade, she never got to settle down in England.
The hardest task for a royal mistress was getting the public to actually like them. Nell Gwyn made that seem almost too easy. She also has a monument in London.
Henrietta of England, known as Minette, fled England at the age of only three, then became a very unhappy duchess, followed by her very mysterious early death.