Many Registry defrag tools are commercial, over the top and some even go as far as stripping too much information from your Registry, causing additional issues.
Quicksys RegDefrag 2.3 is a simple and free Registry defrag and optimisation tool, which is both well designed and simple to use.
This is the brand new 2.x release and ships with a number of new features including a new defrag algorithm, HTML reporting and much more.
Download Quicksys RegDefrag 2.3