Stapelia gigantea. Once the stinky flower opens and the flies lay their nasty grubs, you'll have a positive ID! Have fun! There are a couple of other Stapelia that have large flowers like this one, so wait and post an update with the flower.

And to add to that, it's not a cactus, but it is a succulent! :)

Nancy

Thank you for all of the info!

no fair! mine never got maggots! ;-)

Very pretty!

Laura,
How did you keep yours away from flies? Inside?

Teisa