Prezi’s default font is Calluna. Other fonts used are Liberation Serif, Fertigo Pro, and Existence Unicase Light.
Calluna comes in 8 fonts: Light, Regular, Regular+Italic, Semibold+Italic,Bold+Italic and Black. The regular is absolutely free.
exljbris fonts are available from:
exljbris webfonts are available from: Typekit, Fontspring