With AMD's plans to slim down their offerings and better differentiate which CPUs go to which market, they have made it well known that the Sempron will encompass the entire entry-level line. They will also be pulling the single-core Athlon 64 line, and it may come sooner than initially expected.
AMD has canceled the “Lima” processors, which were to be the last single-core Athlon64 CPUs. Instead, the existing Orleans core Athlon64s will be the last of the line, with all single-core desktop processors moving to the Sempron name.
AMD does have several single-core CPUs planned, with the latest being released in September. However, by the end of this year all non-Semprons can be expected to be multi-core processors. We're already seeing that with Phenom.