In reply to Nick Russell:
Basically any krab will work to an extent, as long as you don't put too many wires on one krab. However krabs with a broad base will work much better.
I've used BD Oval wires a lot. I wrote a review of them a long time ago:
http://www.ukclimbing.com/gear/review.php?id=499
Reccently I've started using DMM Spectre 2s, which have the added advantage of being avaiable in different colours and asymetric. They're also a bit lighter too.
I would strongly reccomend not racking too many wires on one krab.
1) They are far likely to tangle when you are fiddling around one handed in extremis.
2) If you do drop them you've drop them you've dropped most of you wires.
FWIV I rack have 6 wires per krab, split over three krabs. I then have an additional small krab with 8 brass micro wires.
Petzl Spirit, BD Hotwires, WC Helims amd DMM Shaddows are all good racking krabs.