I've heard about schools who don't look at ACT or SAT scores, but are there any cases of colleges ignoring GPA for their admissions decisions?
No colleges ignore GPA completely, but they are less interested in its numerical value than most people think (unless it's dramatically lower than their averages). Colleges tend to focus more on which classes you took and how you progressed throughout high school. Because high schools can vary in quality and in the ways they calculate GPAs, the nature of your coursework is more important than whether you end up with a 4.0.
In other words, the way your GPA is viewed is affected by the context of your environment and the road you took to earn it, but it is always a component of admissions decisions. Your high school grades and choice of coursework provide invaluable evidence of your long-term academic drive and willingness to take on mental challenges. Read this article for more information on GPAs and their role in the admissions process.