Icon: all calendar views (day, week, month, year and agenda) permanently show the today icon in the action  bar. 

Long-press: in day and week view, you can long-press the mini-month-view to go to today.

3-finger-tap: you can configure the three-finger-tap gesture to go to today. 

title-bar-tap: you can configure the title-bar-tap gesture to go to today.