Best interconnects used for around $500 +?

Agree with the Clear Day IC's. I own several pairs and they embarrass many, more expensive cables. They'll bring out the best of you CJ gear that's for sure. Very open revealing cables. Kimber KCAG is a very nice cable and you can pick them up used around $500, but I'd go with the Clear Days and either save the difference or pick up a couple pairs. If you can find a used pair of WyWires Silvers that's a nice step up from the Clear Day Cables, but they don't come up for sale used often. Good luck.

Try the usedcable.com lending library. I did years ago and have settled it was a great help in finding the right cable for my system.

I have been very pleased with Herron Audio cables.  I haven't had any reason to change.  That said, I have not heard a very wide variety of cables.

What interconnects are you using currently and what specifically are you looking to improve upon?

I currently have the Audience au24se interconnects and they are very good.  I've demoed others under 1000 and these were my favorites.  They are very fast, dynamic and neutral.  I have tubes in my system and they were my personal favorites at the 1000 point.  I did demo the Wywires silvers and slightly preferred the audience au24se in my system although in another system the Wywires might be better.  For around 500 the SE's are a great value.