You may want to start by researching BI solutions like Business Objects and Cognos.
Somehow user-friendly, not cheap.
In regards to let users "create their own stuff" I've seen users creating performance nightmares - from "select * with no where clause" to five billion rows join statements - believe me, you should never understimate the ability of an end user when it comes to bring the performance of your database down to its knees.
Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.