Colin Firth (Mr. Darcy, 1995) and wife Livia managed to keep dry on the red carpet. He was nominated for A Single Man.
Caret Mulligan (Kitty Bennet, 2005 & Isabella Thorpe, 2007) brought her mom, and sported a cute hair band. Sadly, she did not win for An Education.
Kate Winslet (Marianne Dashwood, 1996) looked regal and spectacular in an Yves St. Laurent gown. She presented a Golden Globe to Jeff Bridges for Best Actor in Crazy Heart.
And although Emily Blunt (nominated for Young Victoria) has not yet portrayed a Jane Austen character in a film, she is removed by only one degree of separation, having performed opposite Anne Hathaway (Becoming Jane) in The Devil Wears Prada and as Prudie in the Jane Austen Book Club
Mention must be made of Janet McTeer, Mrs. Dashwood, 2007, (Thanks Deborah) for HBO's Into the Storm. Unfortunately, I could find no image of her at the Award Ceremony.