Proc rate is based by your dexterity, and further enhanced by certain effects like
Weapon Affinity and the worn effect: Combat Effects +1 (for example). There are also AAs you can improve your proc rate with.
Offhand weapons proc 1/2 the normal rate.
Reyla E'Xsul, Necromancer wrote:
For mainhand weapons:
305 DEX - 2.0 ppm
205 DEX - 1.5 ppm
105 DEX - 1.0 ppm
For offhand weapons:
305 DEX = 1 proc/min
205 DEX = .75 proc/min
105 DEX = .5 proc/min
As far as we can tell, all proc augments and spell procs follow the above rule for proc rates. Augment proc and spell proc rates DO STACK with a weapons innate proc rate. If you have a standard weapon, augment it and cast a spell proc on it, you will get approximately 6.0 ppm. When adding procs to weapons with innate procs, each successive proc will have an insignificantly smaller proc rate due to the way weapon procs work. Each time a weapon swing, it starts by checking for an innate proc. If the innate proc does not go off, then it checks for an augment proc. If the augment does not go off, then it checks for a spell proc. Since a weapon can only proc once per swing, as soon as 1 proc does go off, the remaining procs will not even be checked.
Courtesy of the Steel Warrior.
Your attack speed has nothing to do with your proc rate. Note that a Dexterity below 105 will proc .5 mainhand, and .25 offhand.
I feel the need to throw out this link one more time to keep it alive;
INFO.
Note: The level cap has changed since this information, so I cannot confirm the proc rate for Dexterity cap increase.