Most common:
* Intéressant (masculine)
* Intéressante (feminine)
Other options:
* Passionnant (exciting, thrilling)
* Attrayant (attractive, appealing)
* Curieux (curious, intriguing)
* Intriguant (intriguing)
* Captivant (captivating)
* Fascinant (fascinating)
You'll need to choose the best translation based on the specific meaning of "interesting" in your context.