If you want to be more informal, you can say "de nada" (no problem) or "no hay de qué" (there's nothing to it). You can also say "vale" (okay) or "guay" (cool) if you want to sound really casual.
Here are some examples of how you can use these phrases:
* Gracias por tu ayuda. (Thank you for your help.)
* Muchas gracias por el regalo. (Thank you very much for the gift.)
* Gracias de todo corazón por todo lo que has hecho por mí. (Thank you from the bottom of my heart for everything you've done for me.)
* De nada, encantado de ayudar. (No problem, I'm happy to help.)
* No hay de qué, siempre dispuesto. (There's nothing to it, I'm always happy to help.)
* Vale, de acuerdo. (Okay, I agree.)
* Guay, me alegro. (Cool, I'm glad.)
I hope this helps!