Quite a few... not even that hard to set up... all things considered, since it was canon he was supposed to choose, and it was then taken out of his hands.
The trick... Ranma must normally be strong enough emotionally to want to enforce that initial decision. Normally, that seems to be done either by crossover, or time travel giving more knowledge than he had in canon.
I assume you also mean making the decision right from the get go. I should note neither side wanted the engagement right away, and neither knew the others... so it really would be too difficult to do that in most normal scenarios.
Some examples:
RANMA 'Bitter Memories Rewrite' by N Reynolds - [Status=Not Complete] - [Last Dld=09/11/2004] - [Size=139kb]
RANMA 'Burning Inside' by Calum Wallace - [Status=Single File] - [Last Dld=05/16/2002] - [Size=53kb]
RANMA 'Dragon's Destiny' by John Tannius - [Status=Not Complete] - [Last Dld=04/08/2006] - [Size=259kb]
RANMA 'Lonely Match' by Cloud-Dreamer - [Status=Complete] - [Last Dld=06/24/2004] - [Size=664kb]
R-DBZ 'A legend reborn' by Trugeta - [Status=Not Complete] - [Last Dld=10/17/2008] - [Size=1114kb]
R-OMG 'The Demon's Contract' by Ringmaster - [Status=Not Complete] - [Last Dld=07/12/2007] - [Size=183kb]
Sometimes, the choice does not work out, like in the following.
R-SM 'The Return' by Josh Temple - [Status=Not Complete] - [Last Dld=10/18/2008] - [Size=2692kb]
I consider the following a odd followup. It allows him to see his choices, not that he had the choice in his own timeline.
RANMA 'Another Rainy Day in Nerima' by rewind gone nuts - [Status=Not Complete] - [Last Dld=04/03/2009] - [Size=515kb]
Most of Puck Silverbreeze stories fall into this category... but most of those are OOC god mode Ranma.
Runner up might be situations like in all the 'Coupled Union' threads on the AA. In those, the choice was made even before series start.