Free Malcolm Kendall-Smith Petition
Malcolm Kendall-Smith is the RAF medical officer who has been court-martialled and jailed for 8 months for refusing to return to Basra to serve in the illegal war on Iraq. I don't know how much good these petitions do, but if you sign it, you will at least let him know that hundreds of people agree with him and support his stance.
Also, as the petition blurb points out, the Nuremberg trials established the principle that saying "I was only obeying orders" is no defence in the case of war crimes. The ruling of the judge on this case undermines that principle. In fact, the manual of RAF law actually states that a serving officer is justified in refusing to obey a command if it is illegal. Having studied the advice of the Attorney-General, Kendall-Smith has (correctly) concluded that the war is illegal, and therefore refused to return to Iraq.
You can also send messages of support to Malcolm via his solicitor: email@example.com or use the MFAW online comments page, and write to John Reid (Defence Secretary) using their online form.