At the moment I'm playing the nice mod "Rise of mankind" It contains a few mod's than you can choose to put on or off before the start of each game. I really like it! It got more techs but it still feels like a normal civ IV game. It got something called "revolution mod" inside. I am still trying the game, but sounds en looks promising. Same goes for the different kinds of road... from carpath (or something like that) until maglevs. Lots of civics added.. anyway I don't know if this is the right place for this toppic.. if not.. please move to the proper place!
if you google on the net you will find the mod for sure btw...
I love to talk about this mod with others.. know what they say about it! Sounds much better and way more fun than Civ V ever will be.
I used to play A New Dawn (it's an expansion for the mod that has even more techs and such). It was quite involved, but I eventually returned to a vanilla+ approach with RevDCM modded to personal taste. I found RoM:AND a little too complicated for casual gaming, plus it didn't help much for practicing for MP. Still, the added content is really great.