Command and Conquer Tiberian Sun
This is the continuation of the Cabal's Return. It continues the campaign, although this campaign can also be stand-alone.
TT's Map Pack is a rather large C&C: Tiberian Sun map pack that adds many new generic multiplayer maps.
Here's a well-made series of maps that picks up where the original Firestorm Campaign left off, at Cabal's defeat.
Containing all of the maps submitted in the last Open Map Competition., it has a great variety of maps.