Ask HN: What are the best tools for doing reports on your data?

What are the best tools out there (open source preferably) to produce reports regularly from our app database?

Like many of you, we track a lot of things in our startup, from analytics to the funnel, to internal business processes. However, periodically we'd like to see other more detailed events for sanity or cross checking, in a report-type fashion. This is the kind of thing that Excel would do nicely, after extracting from our DB (MySQL, via csv), but that's a pain to do periodically. We'd like to see things like a graph of events of type X per day, or per day of the week, or per week, for a certain period. At the moment we have a few reports generated on demand in the admin pages, with our app (in RoR) a graphics library using a fixed set of queries.

What tools do you use/recommend for doing this?