HarperCollins Publishers has a number of romance/erotica books that are currently priced at just $1.99 for the Kindle/Nook:
Dangerous Lover by Lisa Marie Rice (also
Nook)
Dangerous Secrets by Lisa Marie Rice (also
Nook)
Pleasures of the Night by Sylvia Day (also
Nook)
Desire Untamed (Feral Warriors Series #1) by Pamela Palmer (also
Nook)
Everything Forbidden by Jess Michaels (also
Nook)
A Perfect Darkness by Jaime Rush (also
Nook)
Enslave : The Taming of the Beast by Cathy Yardley (also
Nook)
If This Bed Could Talk by Liz Maverick, Kimberly Dean, and Lynn Lafleur (also
Nook)
Forbidden Fantasies by Lynn Lafleur (also
Nook)