Slave to Sensation by Nalini Singh
Demon Angel by Meljean Brook
Nice Girls Don't Have Fangs by Molly Harper
I think that Ms Singh's Slave to Sensation goes without saying. One of the best and most popular series, the Psy-Changelings delivers in every book: great characters, great romance and awesome plots. Each book was key for the overall storyline. Really looking forward to Allegiance of Honor and the next story arc.
What I like about Demon Angel is the different twist Ms Brook has on vampires and angels. Okay, they're not really angels, but still. It was quite refreshing from all the other shapeshifters and vampires books. The romance in Demon Angel was also epic. Something else that's great about The Guardians series is that it's complete! With a very satisfying ending.
Not all paranormal romance books need to be dark. Nice Girls Don't Have Fangs is the best example of that. I consider this fluffy paranormal romance, something that is definitively needed :) Just love the heroine in this one, she's so much fun.
Hmmm, my list is a bit short, but that's all I can think of. What about you? what books would be in your paranormal romance starter kit?