VC (Valhalla Customs) comprises
C3V (Classic Custom Creators of Valhalla) and
SoV (Soldiers of Valhalla).
C3G (Comic Custom Creators Guild) is a project with different goals.
C3V designs, tests, and releases units intended to be fully compatible with classic Heroscape. SoV has a group of judges who test user submitted customs with the same goal. Both are quite rigorous and typically use miniatures from other games. I've worked with C3V and seen how SoV runs things (and even got a submission approved by them).
C3G is more focused on expanding upon the base idea created in the marvel set that was released. Their stuff is not intended or tested to be played with classic Heroscape, but can be. What they have created is a plethora of units with diverse power sets based on recognizable (and less recognizable) existing characters usually pulled from the Heroclix line of figures. It plays somewhat differently than classic Heroscape, but it is very fun, and I'm part of the group that is like the quality control before it starts getting tested.
All three groups are full of excellent people who can direct you to anything you might find interesting. I highly recommend checking them out.
~Dysole, who hopes she isn't overwhelming you with information in her links