Nola,
I usually use my big vise and 3 shoulder bolts hanging over the vise jaws.
I put 2 shoulder bolts on one jaw, spread so as to cover the length of the bend, and 1 shoulder bolt on the opposite jaw at the center or high point of the bend.
Then insert the tool, between the two jaws and 3 bolt and slowly squeeze the jaws together. I find that I have to over straighten the tool just a tad to compensate for the springiness of the tool steel (i.e. over correct the bend).
Then remove the tool and check it for straightness. If the tool still has some bend to it, it's back to the vise & bolts for another round of straightening. Like most things, there are physical limits to this method.
Make sense? Clear as mud?
It's really a very simple method once you see it done or do it successfully; it works well on screwdrivers, prybars, scrapers, chisels, punchs, flat wrenches, and many other bent things.