rakrent.com: Rtsc: The Full Rts Games List
This is a largish selection of real time games with a strategic component, ranging from your classic RTS through to city builders.
glest.org: Glest - The Free Real-Time Strategy Game
Glest is a free 3D real time strategy game, available for several operating systems and that can be modified using XML and a set of tools.
Add Site or Add URL to Submit Site to the Real-Time Strategy Directory