Warzone does look good, downloading right now.
I'm a horrible RTS player but I'd play you anyway marc.
yes - Word War vi -( as in viper,vim,vi)
OpenArena, Savage2(Savage2 has a native linux install and is a online MMORTS). Savage2 is great if you havn't tried it you should, plus its free online play. Which suits Linux perfectly with 32 bit or 64 bit both available.
Savage 2 Download : http://www.savage2.com/en/download.php
OpenArena Download : Use ubuntu software center.