Don't know of any mods but to really make this game shine you should get online for some co-op. I play all the time on SimHQ; they swear to realism, make extensive use of the planning facilities, and have a huge vault of custom-made missions. There should be some games running tonight if you are interested. Here's the sticky on their forums:
http://www.simhq.com/forum/ubbthread...56#Post2498856