I was told that using older versions of Odin sometimes work better then the latest versions. Anyway I'd like to thank you all for the informative replies. I managed to fix it by going into CWM recovery and choose "reboot to bootloader" from the advanced menu.
It seemed to have triggered a download mode which allowed me to flash.
And no, my SD wasn't recognized by anything. Not on PC nor recovery.
Device: Samsung Galaxy SIII GT-I9300
ROM: CyanogenMod 11 Latest nightly
Kernel: CyanogenMod Stock