We say: "De nada". Actually we do not have specially enfatic ways of saying it (none that I can remember at least). However, if we want to make the other person feel more comfortable we use expressions like: "Cuando quiera(s)" (Anytime) / "Ha sido un placer" (My pleasure; in a more formal context).
The tone and a smile will make the difference!
These are some other ways other than the traditional "you're welcome" phrases: mi placer, es mi placer, el placer es mío, gracias a ti, gracias a ustedes, no hay problema, esta vez es la última vez, cállate ya, cállense ya.
You can use the last three with friends who keep thanking you and you just want them to be quiet. I told you I'd give you some non-traditional ways.