Power BI support more then 30+ types of inbuilt visuals and also you can import custom visual from file, Power BI market place or App source.
Custom visuals provides advanced level of customization in terms of design & layout. In app source there are lots of custom visuals are available but all are not certified by Microsoft Power BI.
List of Custom visuals in Power BI-
Enlighten Aquarium custom visual
Cylindrical Gauge by MAQ Software
Calendar by Tallan – Microsoft AppSource