I recently fired up Battlefield 2 again, was missing flying helicopters.
Anyway thought I'd post links to the 2 most popular fun mods for this game.
 
First place goes to.....
http://pointofexistence.com/
 
And coming in at a very close second....
http://www.nawmod.com/
 
In Third place is a different kind of mod altogether...
http://sandboxmod.com/
 
Here are direct fileplanet links to download them if interested...
 
http://www.fileplanet.com/189745/download/Battlefield-2---Point-of-Existence-2-v2.1-to-v2.5-Patch
 
http://www.fileplanet.com/157839/download/Battlefield-2----Nations-at-War-Mod-v5.2
 
http://www.fileplanet.com/172920/download/Battlefield-2---Sandbox-0.5
 
I have all three of these mods up and runnning, and they are all top notch.
If you have any questions about either of these, fire away.
 
Enjoy