Since it would seem there is a good sized fanbase at the .org for text based RTS's, here's one i've been playing for a month now - www.ogame.org

Very fun space based game. It takes forever to get built up, but once you've been playing for a while you end up having massive space battles. Apparently battles among the more established players involve hundreds of thousands of ships.

Currently i have a small fleet of 10 light fighters, 8 heavy fighters, 4 small cargo ships (for taking the loot home!) and 2 cruisers, which completely pwn the enemy defences.

I'm having a small war right now with one of my neighbours. Very fun!

I also have three planets under my control right now, but i'm suffering a bit of crisis with regards to my resources, as they are running very low.

If there's anyone already playing who wants to come and have a spy at me with an espionage probe, my co-ordinates are 1:277:11.