I think the monthly all-in 99p sweep may have run its course, but you’ll still get occasional updates. This month the estimable imprint S.F. Masterworks has a big chunk of classics on at 99p.
A Scanner Darkly – Philip K Dick Inverted World – Christopher Priest Doomsday Book – Connie Willis Roadside Picnic – Arkady Strugatsky Mockingbird – Walter Tevis The Forever War – Joe Haldeman Rendezvous With Rama – Arthur C. Clarke The Dispossessed – Ursula K LeGuin
plus in other editions Neuromancer – William S Gibson Altered Carbon – Richard Morgan Revelation Space – Alistair Reynolds