AS SSD is a great free tool designed just for benching Solid State Drives. It performs an array of sequential read and write tests, as well as random read and write tests with sequential access times over a portion of the drive. AS SSD includes a sub suite of benchmarks with various file pattern algorithms but this is difficult in trying to judge accurate performance figures.
AS SSD uses incompressible data. The Crucial M4 256gb performs above the Corsair Force 3 120gb and OCZ Agility 3 240GB, but behind the OCZ Vertex 3 and ADATA S511 240GB drives.