AMD Sempron 3400+
The Sempron 3400+ 'Palermo' is the fastest Sempron on the S754 platform. Released in 2005 as budget CPU. Not the fastest CPU out there but it was sold at a fair price.
I liked the first 'Athlon 64' based Semprons for being a solid platform and having a low thermal profile when Cool 'n Quiet was enabled.