(at around 29 mins) When Sayid is captured and Locke is talking to him, the amount of iced tea in Locke's glass changes between shots.
When Sayid drops the gun after shooting the man on the golf course, it is not seen on the grass as he walks away.
When Elsa talks in German to her employer in the flash forward scene, the subtitles say 'He had no idea', but what she actually (roughly) says at that moment translates into 'He won't give up the name now'. Earlier in that scene, the subtitles say 'He won't give up the name now', but the actual words translate into 'He won't say anything'. Moreover, Elsa's German is quite bad. She says 'Er wird die Name jetzt nicht aufgeben', which is a literal, non-existing translation from the English 'He won't give up the name now', and wrong on many levels. The correct German sentence would be 'Er wird den Namen jetzt nicht sagen'.
Daniel, Jack and Lapides have no physical reaction to the incoming rocket that lands within 10 feet of them, revealing it to be CGI clearly added later. They should be backing up or even running away, and their eyes should be following it. Instead they stand perfectly still and Daniel even takes a step forward toward the incoming rocket and he is still looking up after it hits.
When Sayid is in the veterinarian's operating theatre, there is a German sign behind him saying 'Wenn Parasiten Auch Die Gesundheit Ihrer Familie Bedrohen', which means 'When parasites also threaten your family'. The capitalization however follows English rules, with all words beginning with caps, which is never done in German language, revealing that the sign is a prop made by non-native speakers.
When Sayid arrives at Elsa's hotel before taking her to the opera, she remarks how nice he looks. He replies, "If a man can't wear his tuxedo by the fifth date, why bother?" But he is not wearing a tuxedo, only a regular black suit and tie.