There's a new addition to my list of Best Water-Soluble Pencils, something I tried for the first time last month: water-soluble tinted graphite created by Derwent (Buy Direct: Graphitint).
Used dry, I liked the underlying earthiness to them, the darkness of the graphite coming through and muting the color somewhat, rather than pure color from colored pencils. When wet, the color is quite intense, though still earthy, and definitely something to be experimented with before using on an important artwork.
Image © 2012 Marion Boddy-Evans. Licensed to About.com, Inc.