dRAMatic is the best memory optimization tool you can find.

It allows you to optimize (not just free) your system memory with its advanced defragmentation and garbage collection algorythms.

It can sit down in your system tray and you can control it through a handy pop-up menu, or you can use the full visual interface to configure it and get a detailed system memory profile.

Main advantages of using dRAMatic are:
It gives you detailed info about your memory
Very small footprint (just ~480 Kb. file size)
It defragments, optimizes, and frees physical and virtual memory
It can be automated using user-defined memory limits