Ski trip

If you guys have a weekend and live near a ski resort (oops, Miami huh?)
Rent a beach house and have a big party, rent a boat and some jetskis, too.
Go to Disneyworld in the middle of the week (less people)
Go on a big shopping spree in the middle of the electronic and clothes shopping area. (This is something the girls would love, guys not so much)
Save the money and go do a BBQ. Then buy nice gifts for everyone.
Split up the parties and go camping with the guys. Let the girls do whatever they want. (This is a good idea)
...There are lots of things you can do, but all of them require a bit of planning and really depends on the people.