Has there been any inexpensive item that enhanced your system's sound?


For me it was an inexpensive power cord that was laying around for years, a Pangea AC9.  I have it connected to my Yamaha A S2000.  I've tried the stock cord on the Yamaha and then some of my other cords, (Wireworld, VH Flavor 4, Acronlink/Oyaide custom cord and a MAC). I've had lots of amps and integrated amps over the years, and this is the first time the Pangea contributed to making better sound. It surprised me because I had tossed it aside and forgot about it.  Power cord performance is such a crap-shoot and dependent on so many other variables in the audio chain.  Any inexpensive item you've come across that enhanced your system's sound? 
foster_9
There are quite a number of very effective tweaks. Of these, I believe the Schumann resonance devices have made the most dramatic positive improvement.
Regarding power isolation, buy products that solve the solution inherently. Insted of chasing it after the fact.  The line currently offered by Vinnie Rossi are an amazing all in one solution. I have a VR120 that is sublime. Lots of power/current and puts out such an organic relaxed sound. 
Four Herbie's Audio Lab "Big Fat Dots" under each of my KEF LS50 monitor speakers that sit on home made concrete block speaker stands.
There's always wrapping the transformer with mu metal.  Low frequency high permeability mu metal.

The last couple of dedicated listening rooms I've put together I've focused a lot more on acoustic treatments.  Different kinds of inexpensive treatments such as thick drapes, diffusers, Auralex foam wedges, Acoustimac panels, ASC tube traps etc.. Usually all purchase used.  Trial and error for best performance.

The ASC tube traps have made the biggest difference in my system and were a paradigm shift in performance in my room.  Very impressed.