For a general statement:
* J'ai trouvé: This is the most common translation, meaning "I found" in the past tense.
For something you just found:
* Je viens de trouver: This translates to "I just found" and emphasizes the recency of the discovery.
For something you discovered by searching:
* J'ai découvert: This means "I discovered" and implies a more deliberate search.
For something you found unexpectedly:
* J'ai trouvé par hasard: This means "I found by chance" and emphasizes the unexpected nature of the discovery.
Let me know the context and I can give you the most appropriate translation!