Bare in mind the MPH speed figures quoted at the lower part of PAXfips post are "inertial" speeds. I.E cumulative speed of the vehicle + earth rotational velocity from west to east.
Before launch the vehicle is travelling 914.4 MPH due to the earths rotation.
If you open the link posted by PAXfips and look at the top section, the 6th column from the left will give you the orbiters "local" speed and the 7th column the "inertial" speed. e.g at 10 secs after liftoff "local" speed is 126.8 MPH and after 30 secs speed is 495.7 MPH.
