Also Algebraist by the same author Ian Banks - there is a species living so slowly, that star travel is practical for them, so they are ubiquitus in the whole known universe.
Also one of the intelligences encountered in Diaspora by Greg Egan.
Actually, they just meet a localised handling agent that explains that they work for a star-spanning sentience - which is something the characters had been considering as a way of making themselves robust against civilisation-destroying gamma ray bursts, but dismissed on the grounds that it made everything so slow - though that links into the other theme in that book of simulated beings existing on very different timescales.
