Clever Keys is a python script that aims to make keying in Maya easier and more intuitive. It will only key the channels you have selected and try to insert keys whenever possible, leaving your curves alone.
Now a part of Guppy Animation Tools!
Good Parenting was a script made to deal with constraining a large number of objects. It was made primarily for riggers, but with the hope that it would be useful for anyone who needs to constrain more than a few nodes. It has many periphery functions in addition to constraining, such as buffering nodes, moving pivots, and connecting attributes.
Smooth Mesh is a plugin deformer for Maya. It averages the verticies of a polygon mesh and can attempt to maintain volume. Since Smooth Mesh is a deformer it is paintable and has an envelope, unlike Maya's average verticies function. This is more or less the first plugin I have ever written and should be considered extremely experimental!