So far the only way I know to say "I'm sorry" is "lo siento." However, this gets repetitive rather quickly, and sometimes I'm looking for a stronger form of an apology. What other ways are there to apologize in spanish? If you are apologizing for an extremely terrible thing you've done, would you use a different phrase? How do native speakers apologize or convey regret for things they've done?
Well at least in Mexico is not common to say "lo siento" instead we say "perdón" for apologizing. The only part that I've heard "lo siento" is in movies or telenovelas.
A stronger version of "perdón" is "perdóname" or "discúlpame". You can add "por favor" at the beginning or at the end of the sentence.
Here some examples:
In Argentina, we just emphasize "Lo siento" (or "lo lamento")
Alfredo's alternatives are also ok.