Strategic games for Co-op online

[Pregno]

Hi everybody!
It's my first message in Steam Community. I tried to search for something similar to my question but I didn't find anything, so here we are!
Can someone suggest me a strategic co operative game to play with a friend by internet (not local). The better suggestions may be RTS, realistic gameplay or dinamic gameplay (no slow gameplay).
I would thank you already for your help and I hope my english isn't so bad.
Bye!

[Captain Pentium]

Alien Swarm Reactive Drop isn't an RTS game but can use strategy depending on your playstyle.

[Gwarsbane]

This is the suggestion or ideas area to make the Steam program itself better, this is not a suggestion or idea for the Steam program.

Try posting here
http://steamcommunity.com/discussions/forum/12/