On the subject of MTW mods;
There are many greatmods for many periods:

Hellenic Total War for fighting in ancient greece. A mod of the highest standards.

Napoleonic Total War for early 1800's fighting. Another amazing mod.

Samurai total war for a Shogun TW total conversion.

For improvements to the medieval era, the three main mods I know of are the XL mod, BKB's Super mod, and WesW's Medmod. These are all great mods, and all slightly different. If I had to choose one, it might be Medmod, but if you have the hard drive space I suggest trying all three.

And there are many other mods out there.

If this was about RTW mods; You might want to wait a little until BI comes out and get a combo pack. As it is, RTW is not that mod friendly.
There are some very good mods (Rome total realism, Europa Barborum, Chivalry total war, and others) Alas, all are hampered by many hard coded limitations.

Crazed Rabbit