Depending on your DC's track record with standardized tests, I would start with the official ACT Red Book (which consists of 4-5 old tests), and have DC practice taking the individual sections -- and then hire a tutor to address specific weaknesses, especially with math and science. Timing is a much bigger challenge with the ACT so getting used to the pace in advance is absolutely key, and you don't need a class for that. My DCs also liked the Barron's ACT 36 guide. College Confidential has lots of information on ACT prep, so you could peruse that for other resources and tips.

Also CD (for a pc)
Geez auto correct! !

ACT not active

When I wanted to prep for the ACTIVE I just bought a COKE from Best buy and ended up doing pretty well. This was 10 years ago though.

Kaplan? Princeton? Which or any other service do you recommend?