For knocking out fairly "run of the mill" reports, SQL Reporting Services is really quite impressive.
For complicated analysis, loading the data (maybe pre-aggregated) into an Excel Pivot table is usually adequate for most users.
I've found you can spend a lot of time (and money) building a comprehensive "ad-hoc" reporting suite and after the first month or two of "wow factor", 99% of the reports generated will be the same report with minor differences in a fixed set of parameters.
Don't accept when a user says they want "ad-hoc" reports without specifying what goals and targets their looking for. They are just fishing and they need to actually spend as much time on THINKING about THEIR reporting requirements as YOU would have to spend BUILDING their solution.
I've spent too much time building the "the system that can report everything" and for it to become out of date or out of favour before it was finished. Much better to get the quick wins out of the way as quick as possible and then spend time "systemising" the most important reports.
