There are some excellent C&C mods available now. Here's two:

Combined Arms is a Red Alert mod that brings in GDI and Nod and does a lot of interesting things. Campaigns for all factions as they deal with the upheaval that is a second war being overlayed over the war they were fighting.

Mental Omega is a Red Alert 2 mod that reimagines the expansion pack, Yuri's Revenge. Heavy faction overhauls and a full campaign. There's also a second mod that goes on top of it that remakes the entire Red Alert 2 campaign using the improvements of Mental Omega. It tells the same story, but all of the missions have been recreated with more complex and varied design.