Damn, couldn't find my cable receipts. here's some other examples of the markup though (BB makes all their money on accessories and warranties)...
Xbox wireless controller. retail $39.99, employee: $19.16
Leather notebook case. retail $49.99, employee 12.86
Laptop chill pad (goes underneath your laptop, has 2 fans). retail $49.99. employee 23.63.
Secure Digital 512 MB memory card. retail 79.99, employee 51.88.
Secure Digital 1 GB card. retail $119. employee $74.06.
Thermal sensing cooling fan. retail $19.99, employee $2.45.
Tivo. retail $199.99, employee $99.99
Toshiba DVD player. retail $179.99, employee $132.46
Damn, I wish I still had the cable receipts so I could scan and post for you, before I left I bought 2 firewire and USB cables each for myself and my parents, brothers, and sisters. I bought a total of 20 cables and it cost me less than $40.
The best margin for Best Buy in computers are any of the in-house brands (i.e., Dynex, Geek Squad), home theaters it's the Monster cables (Monster Corp. is owned by BB), that's about all I know or cared about (worked in computers, and had some friends in home theater).