For a brief time in the history of home-built gaming PCs, the "rounded cable" was a premium accessory. The wide, flat ribbon cables that connected hard disk and CD-ROM drives to the motherboard impeded air flow, making it difficult to achieve an ample breeze over your overclocked Athlon. Because they were a speciality part, rounded cables were expensive — especially considering standard IDE cables were usually bundled for free with motherboards — which forced many to put down the Mountain Dew and take up an X-Acto knife to make their own. Soon the market fixed the problem. Rounded cables are now inexpensive — and obviated, since SATA uses a small, thin cable by default.
But out there in the world of computing there are still folks who need to make ribbon cables of their own for custom installations. And as a failed sysadmin myself, I've lost most of my knowledge of Cisco router commands but retained a fetish for cabling tools, like this ribbon cable cutter from Knipex that can slice through the delicate bands without crushing the individual strands. I also like it because the picture has a rainbow.
Street prices are between $60 and $100, which can buy a whole crate of pre-made ribbon cables of various length.
Knipex Ribbon-Cable Cutter [Toolmonger]