The Algebraist, by Iain M. Banks

A standalone science fiction novel

In the past I've found Iain Banks' Culture novels a bit too weird for my taste, but The Algebraist (not a Culture novel) is excellent. It is set in a far future, and with plenty of history behind it to drive the plot (billions of years of it, in fact). Humans are one of the few races allowed to communicate with the extraordinarily long-lifed Dwellers (one of the "slow"). This is the story of a triangular clash between the Dwellers and several "quick" cultures, eager for technology that the Dwellers may or may not have.

Highly recommended.