So, the first one is...
Woke Up on Venus
(suggested by the ever-popular "Woke Up in Vegas")
The hero, heroine, or both wakes up on Venus with no memory of the day or so (if they were already there) or couple of weeks (if they were previously on Earth), and is surprised to discover that they're (a) in an isolated cabin with a member of the opposite sex they don't recall meeting and (b) married.
This may be the result of too much booze, a fiendish plot of some sort (likely if one or both are rich), or an unusual scheme for getting Venus colonised.
So - anyone got any suggestions for more? I'm not looking for plots this time, more general concepts for romantic subplots etc.