Here are some options, depending on the context and the emotion you want to convey:
For surprise or amazement:
* அடடா! (Adada!) - This is a common expression used for surprise or disbelief, similar to "Oh my!"
* ஏய்! (Ey!) - This is another common expression used for surprise or amazement, often used with a rising intonation.
For shock or awe:
* கடவுளே! (Kadavule!) - This literally translates to "God!" and is used to express strong emotions like shock, awe, or disbelief.
* சர்வம்! (Servam!) - This is a more archaic expression meaning "everything!", used to express overwhelming feelings of amazement or disbelief.
For expressing disappointment or frustration:
* என்னடா! (Ennada!) - This is a common expression used to express disappointment, frustration, or disbelief.
Remember that the tone and context are very important in conveying the intended meaning.
It's also important to note that many Tamil speakers use English phrases like "Oh my God" in everyday conversation.