simonw,
Welcome to JDEList! Be sure to include you system configuration in your signature line so that answers can be tailored to your environment.
You have asked a very broad question, to which everyone will have their own answer/opinion. Having run Crystal Reports XI with our JDE system for over 5 years, I'd say that this was one of our best investments ever. It works great for us -- I.T. and a small group of power users create both ad-hoc reporting and standard reports (which can join multiple tables/views, summarize, include graphics, have conditional formatting, etc). I would strongly recommend that anyone looking for reporting solutions look at Crystal Reports along with other options.
You can search JDEList for other postings about reporting solutions for additional details. Good luck in your search.