Free transitions for Vegas Pro. Some of them are plugins, other are only templates.

SMCubes transitions.
It’s a freeware transition. It divides the screen into cubes and ‘explodes’ them outwards spinning them around and recombines them back to the transitioned shot.
http://www.scomo.co.uk/
SMLuminance.
SMLuminance is a freeware transition. It blends from one shot to the next based on either:
a) the luminance of a bitmap (for users of older Vegas versions which don’t have the built-in “Gradient Wipe” transition), or
b) the luminance of the incoming & outgoing shots (which simulate a film-like optical dissolve).
http://www.scomo.co.uk/
AAV ColorLab.
AAV ColorLab is a free plugin, but also three contain transitions:
  • Fade
  • Additive dissolve
  • Substractive dissolve

http://aav6cc.blogspot.com/

Transquare Free Demo Pack from Vegasaur
2 free animated matte clips (3D cube transitions)
Full HD QuickTime movies in Photo Jpeg format
The duration is 1-3 seconds
Includes free poster
Their are templates, not a plugin!
https://vegasaur.com/free-3d-cube-transitions
Free transitions for VEGAS Pro from Vegasaur
11 free transition templates (.veg files) for VEGAS
Easy to use: just drag and drop!
Their are templates, not a plugin!
https://vegasaur.com/free-vegas-pro-transitions