I am going down to Marco next week and I am thinking about taking the Key West Express down for a couple of days. What would be the best site to get the sea conditions? My wife wouldn't like the ride if it was to rough.

I use this.
You can get the marine forecast and click on the buoys way out there to get live sea conditions.
http://www.capeweather.com/buoy-data-florida.html

This one is good too.
http://www.nws.noaa.gov/om/marine/zone/south/keymz.htm

Thank you.