I just replaced my standard large gauge monster speaker cables with a set ofAudio Magic Sceptor II 12' (spade ends), 84.50 from WWW.hcmaudio.com. I wasn't expecting much of a improvement, just a noticeble improvement.

Improved base and mid range response (about 10 to 15%) if I had to put a number on it. The high end actually decreased (about 5 to 10%). This was exactly what I was hoping for as my system is on the bright side and low on the base end.

Acurus Act3 pre-pro
ATI 1505 Amplifier
JBL 4312A Main speakers
Kenwood 5300 FM Tuner (anolog)
Sony 5000 DVD/CD