Try talking to them and listening to each ones cause for the argument and point out where each one has had their reaction fuelled by the others action (usually the case with my two, age 8 & 6) I end up feeling like Judge Judy.
Failing that I separate them into different rooms to play on their own and they soon miss each other. Or, if I get to the stage of getting seriously peeved with them, I leave them to it and go to my bedroom & read a book after making sure all is safe to leave them alone downstairs. They soon miss me and join me where all previous arguments are then forgotten.
Sending them to bed does not work as they just sneak to each others rooms to chat. Time out does not seem to work so well now either. Confiscation of drawingstuff(DD) or the playstation/Wii(DS) works quite well, but I reserve that for major league issues.
If anyone else has some ideas too it would be appreciated.