This shows the result of using six free Final Cut Pro plugins from Alex4D. They are based on built-in plugins - with added controls.

They all have curve controls that allow you to make transitions start, change and finish slowly or quickly. Dissolves are more subtle if they start and finish slowly. Zooms can work better if they start quickly and finish slowly.

This demo shows each transition, then shows the default 'ease-in'/'ease-out' curve that produced the effect.

The transitions are

Cross Zoom + curve (+control for start and finish position)
Spin3D + curve
Spinback3D + curve (+control for background colour)
Swing + curve
Zoom + curve
Cross Dissolve + curve

To get these transition plugins for Final Cut Pro and Final Cut Express, go to alex4d.com and follow the
'Final Cut Studio - plugins and more' link