The IBM Web Accessibility Checklist is extremely thorough. It provides an extensive guide on using the list itself, as well as current WCAG 2.0 checks which are mapped to the upcoming 508 refresh. It also includes legacy requirements for the current version of Section 508. Yay backwards compatibility!
If you’re not comfortable with reading through WCAG 2.0 and its related documentation, a good checklist can be a great place to start. It doesn’t substitute for the guidelines themselves, (sorry, you’re going to have to bite the bullet and become familiar with them), but it can guide you through changes you may be making to your websites or web applications to ensure that the changes you make are also as inclusive as possible. A good checklist can also serve as a template if you’d like to create one for your own organization that specifically reflects your workflows and practices. If you need a guide to the basics of what should be part of any accessibility checklist you create, this post on the defensibility of accessibility checklists contains a high-evel view of what should be included.