Humectancts - Retain moisture and absorb water. A must have for any conditioner.
Panthenol, vegetable glycerin, sorbitol and honey are a few of the popular humectancts to be looking for on the label.
Proteins - Repair and protect hair. Proteins can build up on some peoples hair and is morel ikely to happen with healthier hair. If you experience build up alternate with a protein free conditioner. Some common proteins to look for are soy, wheat, silk, keratin and amino acids.
Moisturizers - Softens and helps reduce frizz in dry hair. Amino acids and aloe vera are two common moisturizers.
Emollients - Add shine and soften hair, emollients also smooth the hair shaft. Common emollients are vegetable oil and nut butters, others are liposomes and glycerides.
My favorite Conditioner to Co-Wash with is anything out of the Suave Naturals line. They contain no silicone so it won't result in residue and build up. They are also priced very friendly at about $1-$2 a bottle.