Speedbreaks, as they have been dubbed by players, are increases in attack speed achieved at certain amounts of DEX. However, speedbreaks change with level. Most speedbreaks give about 4% attack speed. Every kind of weapon, including wands, has speedbreaks.
These tables were all calculated for characters that are level 60. They assume no bonuses to the DEX or attack speed of the user other than their basic stats. At level 90 the third speedbreak and all speedbreaks after it are 1 point of DEX lower than listed here.