Crystal and Halo

 

These are two very underutilized characters, in my opinion.  They are both pretty powerful and have interesting back stories.  There have been very few solo stories featuring them, usually they are in a team setting.  I think that there's plenty that can be done with both by featuring them in some solo adventures and allowing them to really shine.  With the way comics companies are streamlining these days, who knows if that will ever happen.