I especially liked the Zu Mobius and Headphile V2 in my system with a Corda HA-2 amp. The Silver Dragon can also sound marvelous with a synergistic front end but a tad to dry in others. I think with cables it's mostly trial and error; hard to predict the outcome without first-hand (and long-time!) experience in your own setup.
I'd say that from the cables I've tried, the Zu Mobius and Silver Dragon were the technically most capable ones but I preferred the Zu's tonal qualities in my setup. There are three reviews by JaZZ, Tuberoller and Ross, which are definately worth reading when looking for a good HD650 cable.
Finally, there's also the extravagant and risky approach. Get a pair of HD650 connectors, a high-end interconnect and ask a professional or experienced Diyer to tailor you a HD 650 cable. I'm planning on doing this but it's obviously hard to predict the outcome and is quite a gamble since the interconnect will be wasted.