We are after-schooling DD11 in math (total lack of challenge at school). She is finishing Algebra 1 and will soon be moving on to Geometry.

Anyone have a suggestion for a textbook that was worthwhile?

I hear great things about Harold Jacobs' Geometry text:

http://www.lamppostpublishing.com/mathharoldjacobs.htm

That is what we plan to use in a couple of years.

Art of Problem Solving has a very challenging Introduction to Geometry book that worked well for DS12. Their Introduction to Algebra is excellent too. Not a bad idea to get that and see how well she understands algebra. It goes through Algebra 2.

See their web site for information.

Regards,
Jon

Did you try Khan academy?

I've tutored from Jacobs and it is good. We're using Singapore math books, which I prefer myself, but they might be hard to "jump into" at that level, especially since they mix Algebra and Geometry instead of separating them into their own books.