Magic Bullet and NewBlue FX are 2 really great plugins with a lot of good transitions.
I tried Boris FX and it sucks tbh, probably because I just don't like this program in program stuff...
Magic Bullet Misfire is great for "oldschool/grindhouse" editing. It has almost every film damage effect inside(grain/dust particles/displacement etc.).
Another idea would be using the pan/crop mask. You can create your own transitions with it. I saw a tutorial anywhere long time ago.
Check
http://style-productions.net I think it was there anywhere.