Scenarios,cities,other files.
http://caesar3.heavengames.com/downloads/

I was just about to post that here; good thing you have already done so.
Also, there are strategies, walkthroughs and such stuff on that site (other than the downloads section).

good site. I'd recommend that too. There used to be one on geocities called "Which way to Rome?" by Grumpus The Elder (he also had one for Pharaoh called "Which way to Thebes?"sadly it is gone now.
But the heaven games site is a good one to look for tips.

Mirrors of the old Grumpus' sites (and some more stuff) are on my site http://www.villages-and-cities.de/.
http://www.villages-and-cities.de/extern/grumpus/which_way_to_rome
http://www.villages-and-cities.de/extern/grumpus/which_way_to_thebes