Gabaldon, Diana

Billington, Rachel - Theo and Matilda

Deveraux, Jude - Legend 
Deveraux, Jude - A Knight in shining armour

Erskine, Barbara - Lady of Hay
Erskine, Barbara - On the edge of darkness 
Erskine, Barbara - Midnight is a lonely place 
Erskine, Barbara - Child of the phoenix

Flannery, Constance O'Day - Timeswept lovers

Frank, Suzanne J. - Reflections in the Nile

Howard, Linda - Son of the morning

Lee, J. Adrian - Son of the sword
Lee, J. Adrian - Outlaw sword

Moning, Karen Marie - The Highlander's touch
Moning, Karen Marie - Kiss of the highlander

Riley, Eugenia - Tempest in time

Rivers, Francine - The Scarlet thread

Sommers, Lilly - When shadows fall

Tuten, Frederic - Van Gogh's bad cafe

Weyrich, Becky Lee - Swan's way

Willis, Connie - Doomsday Book
Willis, Connie - To say nothing of the dog

If you like the feisty characters, historical detail and romance in Diana Gabaldon's novels, you may also enjoy the following books. However, these titles do not feature time travel. 

Donati, Sara - Into the wilderness

Dunnett, Dorothy - Francis Crawford of Lymond series

Kaufman, Pamela - Shield of three lions 
Kaufman, Pamela - Banners of gold

Pargeter, Edith - Marriage of Meggotta 

Penman, Sharon Kay - Sunne in splendour 
Penman, Sharon Kay - Here be dragons

Seton, Anya - Katherine