GED Study Guides, Comments/Suggestions

My daughter is going to study for her GED this coming school year. I have found a lot of practice tests online, a free online GED and college prep course and I purchased a McGraw-Hill’s GED Study Program.
I just wondered if anyone had any suggestions for workbooks, online sites or other study material that may also help.

I took it last year and used a few different guides. For me, they were all about the same - just take as many practice tests as you can. Practice makes perfect.