This is a plugin with a number of little tools for modelling with more precision:
Draw Box, Draw Cone, Draw Cube, Draw Cylinder and Draw Sphere enable the user to pick 2-3 points to define the size, position (and rotation in some cases) of the standard polygon primitives. Draw box requires 3 points (corner point, length, width) , the others two (centrepoint then size).
The two transform tools mimic common cad tools: the 3 point rotate and the 3 point scale.
1. Select an object or or number of them.
(Use CTRL to snap to elements, Left-click to select all points.)
2. Pick the origin about which the scale or rotation will be done.
3. Pick the reference point (usually on the object to be transformed) that will be used for scaling/rotation
4. In the case of the rotation, pick a point which defines the axis of rotation.
5. Finally, pick the new position for the reference point. Right-click to exit when finished.
Click on this thumbnail to see 4 point rotate in action.
EDIT: (link updated. - download and replace file from .txt to .xsiddon) here.