It really depends on what you want.

There is one here at Simviation.  It's called FS2004 Air Force One and AI Tomcat package.  Get it here!

[url]http://www.simviation.com/fs2004misc4.htm[/url]

Also there is a very good Air Force One by Melvin Rafi here, however, it's a FS 2002 aircraft and may need a bit of "tweaking" to work well with FS 2004.

[url]http://www.simviation.com/fs2002jets85.htm[/url]

There is a very nice FS2004 Air Force One Boeing 747-200 Model by Project Open Sky repainted by Bill Kovatchev.  The file name is OS742AF1.ZIP and is available at another website.  

[Cough*Flightsim.com*Cough.]

These are very nice birds if you want to fly them yourself.

If you're like me you'll like to do something a little more challenging.  I have an AI Air Force One that I picked up at the Project AI website.  I create different flightplans for it using Lee Swordy's excellent Traffic Tools program.

Myself, I like to "escort" the Air Force One with Dino Cattaneo's F-14B Tomcat or Kirk Ollsen's F-16 Viper.  Much like the Air Force One and AI Tomcat package I mentioned first above.  The way I do it gives me the latest aircraft to fly "escort" with.