Star Wars sublight speeds - Yavin
Possibly the most widely used evidence for calculation of sublight speeds in Star Wars is the Death Star approach sequence before the battle of Yavin, in "A New Hope". Here is my two cents on the whole deal.
The Death Star (at one planetary diameter orbital radius) has to cover an arc distance of 453,615km in thirty minutes. Assuming a standing start, it would have to accelerate at a minimum of 280m.s-2 (28g) to get to firing position on the moon Yavin IV.
The X-wings (assuming a hyperspace jump to shorten the distance) also have to travel a minimum of 453,615km around the gas-giant (a fraction of a full orbit) towards the Death Star, in only ten minutes, and stop turn around and match velocities with the Death Star, which by this stage (25 minute point) is travelling at 420km/sec towards the Rebel fighters. To accomplish this, they have to accelerate for five minutes towards the DS, turn around, and accelerate towards the DS for five minutes, at the end of which they must be travelling at 420km/sec, and match accelerations with the DS to maintain position during combat (28g towards Yavin IV). The performance requirement for this feat places their acceleration at about 504g (minimum) and they reached speeds of 1520km/sec in about five minutes during this period.
So we can see, that using ultra-conservative calculations (i.e., assuming hyperspace jumps, etc) a rebel fighter has a minimum acceleration of 5km/s^2. Another source of conservatism is that I used linear acceleration for the calculations, and did not take into account the angular acceleration required to maintain an orbital distance around the gas-giant.
There is no evidence either from the film or the canon novelisation of "A New Hope" that such a hyperspace jump occured. In fact in the book "The Last Command", an extensive battle occurs in the star system which is home to Coruscant, and Republic fighters and ships launched from orbital facilities engaged the Imperial forces in the outer system without doing hyperspace jumps, indicating that such jumps are unnecessary within the confines of a star system. If we were to include the distance from the gas-giant Yavin to it's fourth moon, and similarly allow the Rebel fighters only ten minutes to negotiate this distance, then the fighters acceleration figures approach about 130km/sec^2.
We also know that the fighters were performing well within their capabilities, since there was no unnecessary urgency about either the briefing, the conversations which followed, or the approach to the Death Star.
More Canon Facts
From this, we can deduce that the straight line performance of X-wings, TIE fighters, the Millenium Falcon, and ISD's are all in the same ball-park, although turning ability and maneuvrability varies considerably, with smaller vessels obviously doing better in the maneuvrability stakes.