Most Effective Tweaks

Self explaintory thread. Im looking to experiment with my system and see if I can truly alter the sound of my music with some simple cheap tweaks. If we could all list as many sucessful tweaks as we can to help develop how our systems are put together. Everything to ball bearing isolation to "amber beads" please share your experience and let us know which tweaks you found the most effective or the most dramatic change.

cheers