Looking for a book with a modern character aiding an ancient society.

I'm looking for a story where the main character(s) uses modern knowledge in an older civilization. Others I've read an enjoyed include:

1632 by Flint, which is about a town pulled by in time to an alternate German that uses it's knowledge to aid the local peasants

Earth's New Timeline by Fielding, which is about two men sent back in time to introduce technology faster so that Earth can save itself from an asteroid

A Drive Through Time by Saygo, which is about a man sent back in time with his RV who uses his knowledge to aid the Celts

Matt Miller in the Colonies by Rose, which is about several people sent back through an experimental mishap who are trying to alter history in various ways –I liked this story idea the least

A Ripple in Time by Zugg, which is about a plane group that goes back to early America – for whatever reason I'm having a little trouble getting into this one

First Lessons by Potter, which is about a woman reincarnated in an alternate Medieval World – she was a little too much in her head but the story was good

Marooned in 1799 by Hurst, which is about a family sent back through a natural phenomenon – not in the same vein as the others but I still enjoyed it

The Warp and the Weft by Dahners, which is about a woman with an ability to jump to parallel worlds

Cast Under An Alien Sun by Thorensen, which is about passengers on an airplane rescued by aliens and sent to another world – sometimes heavy on the details but the story was enjoyable

Anything along these same lines would be great.