When "Reports" Aren't Enough

Can anyone give me some pointers as to what business reporting / analytics tools and packages should be used when Reporting Services and Excel are insufficient?

Following the successful deployment of a new application at work in August, we (that is, the IS dev team) have been occasionally requested to provide various reports on the underlying data. So far these have generally been provided using SQL Reporting Services (available online and sometimes emailed to a distribution list as Excel export), and it's been working really well for most requirements.

But as ever, the more you provide, the more the business asks for, and now I find myself faced with a request to produce a huge (in terms of number of rows) Excel report containing, effectively, a few key tables from the database joined together. I contend that this isn't, strictly speaking, a report request - it's a desire to be able to query and filter the data using a familiar tool, but the sheer size will make this infeasible in Excel, and there must be better ways to achieve this goal.

I hear the term ProClarity banded around, and Jez told me about Cognos Reporting - anyone got any experience of using these?  Or recommendations for other useful tools?  Ideally I'd like to be able to give the relevant folk in the business direct read access to our SQL database (or a replica - don't really want people querying the same db used for OLTP), but I'm unsure if this is feasible.