Not all journals are equally appropriate for your work, so you'll want to research the journal before signing the publication agreement. You can read their website, look at print issues, see if your institution subscribes to the journal already, and talk to your colleagues and librarians.
It's true that charging fees for open access publishing may seem counterintuitive. It's supposed to be free, right?
However, fees are often necessary to cover publication and editorial costs, the costs of the double-blind peer review process, and the technical requirements for hosting articles and making them available online.
If you can't afford a publication fee, many publishers offer waivers. Your grantor, institution, school, or department may also have funds budgeted to help faculty and staff publish in their fields.
Within the topic of open access publishing, there is concern about "predatory journals," which are generally defined as journals that purport to provide open access and charge a publication fee (sometimes an excessively high one), but do not provide the same level of editorial attention and peer-review process as a reputable journal.
There's no one list or tool that will tell you which open access journals are "predatory," but here are some resources to help you understand and vet a journal before publishing in it. You can start with Declan Butler's checklist:
Buyer beware: A checklist to identify reputable publishers