These aren't really plots. I'd like to turn them more into plots with your help, but here are a few ideas I'd really like to work with right now.
An Arranged Marriage
This could go a few different ways, but here's one I'd really like to work with: My character wakes up one day to discover she's engaged to someone she's never met before and she has to marry him the same day. The roleplay starts at the wedding where they see each other for the first time. There's the "love at first sight" type and the "I hate you, then love you" type. I'd personally like to do both.
Brother x Sister
Two siblings, a prince and a princess, were betrothed to someone else when all they really wanted was...each other.
The second roleplay is about two normal siblings who just happen to like each other. They get along so well that they start arguements so no one gets the wrong impression when they secretly flirt behind closed doors.
Imaginary Friend x Human
She was a lonely girl. One night she drew a picture of her soul mate. The next day she wakes up to him there.
Prince x Maid
The prince was engaged to a princess, but he was secretly in love with her personal maid. It can become a love triangle or she can simply become his mistress. I'd like to do this both ways.