I have used a couple of different sets of 20' and 30' Mogami cables and enjoy them. Hard to go wrong for the money. You can always use them as a reference if you want to compare something else later.
I have used Redco Audio to do custom lengths and terminations with good results.
http://www.redco.com/Custom-Cable.html
Redco did all my custom DB25 cables here in the studio. I have a few 100 footers between the rooms. Excellent service and top notch quality!