Code Geass

The Code Geass watch order runs two 25-episode seasons, five OVAs and four movies, and this is the correct order to fit every side story in place. Start with the first 25 episodes, Lelouch of the Rebellion, then continue straight into the second season, R2, which runs another 25 episodes. With the main story finished, move to the OVAs: the Special Edition Black Rebellion and Zero Requiem recaps, Kiseki no Tanjobi, Nunnally in Wonderland, and the Boukoku no Akito arc. The four films come last — the Hangyaku no Lelouch recap trilogy (Koudou, Handou and Oudou), which condenses both seasons, followed by Fukkatsu no Lelouch, the true sequel film set after Zero Requiem. If you only want the canon through-line, the two seasons plus Fukkatsu no Lelouch are enough; the OVAs and recap trilogy are extras you can add for completeness.