Livecurlylivefree.com has the best explanation of co-washing I've seen anywhere, in terms of the technique and such.
I also tend to get oily grimy roots, and while CG didn't eliminate it, it did seem to make it better (part of this is that I do intense martail arts 3-5 days a week for 2-3 hours a day). The important thing to remember is that there are countless ways to tailor CG to work for you (and that doesn't even count the realm of "modified CG").
I would recommend using a very light conditioner to co-wash and a richer conditioner to use as a traditional rinse-out conditioner. My personal favorite for co-washing is VO5 Vanilla Mint Tea.
If co-washing doesn't work for you (and it doesn't work for everyone), you also have the option of a cleansing conditioner (like Deva No-Poo or Curl Junkie Daily Fix) or a low-poo (sulfate-free shampoo- tons of options). Many people, especially with finer textured hair, will switch between these three options as needed.
Modified CG since 11/5/11
CLEANSE: VO5 Vanilla Mint Tea Clarifying, DevaCare No-Poo, CHS Treatment Shampoo
RO: DevaCare One Condition, SS Caitlin's Conditioner, Mop Top Daily Conditioner
LI: SS Repairing Protein Treatment, CHS Silk Leave-In
STYLE: Re:Coil, Curl Keeper, Deva Ultra Defining Gel, Curls Rock Amplifier and Strong Hold Mousse, Sweet Curls Elixirs Okra Gel and Hard Hold Gel, SS Curl Enhancing Jelly and Firm Hold Gel