Definitely SQL*PLUS, you're right.
I managed to create a report as a UNION select between data and SUMs of data queries, with relevant fields for GROUPing and ORDERing. I would have liked to be able to get these "relevant fields" shown only once, so I started to check what is available, and stumbled over Oracle's approach.
I'll have a look at the suggested reporting tools.
Thanks,
SxN