Blood and Steel is a good SP mod (Turns the game into a Calradia with demons wandering around, also completely reworks the factions:
http://forums.taleworlds.com/index.php/board,185.0.htmlThe Red Wars is a great one also (Brings Calradia into the years before World War II, with Communism and Fascism clashing):
http://forums.taleworlds.com/index.php/board,366.0.htmlBut here's some mods to keep an eye out for once they're released:
Nova Aetas (Late Renessance game, think same time period as AC: Brotherhood(This mod has a metric shitton of features, it's insane)):
http://forums.taleworlds.com/index.php/topic,281485.0.htmlCalradia Imperial Age (Mod which converts Calradia into the Napoleonic Era, adds some new nations too)
http://forums.taleworlds.com/index.php/topic,307638.0.htmlL'Aigle (Most hyped Warband mod in existance, been in production for years and has had many delays. Still, converts the entire era to 1809 Europe and a good place to grab some eye candy):
http://forums.taleworlds.com/index.php/topic,195571.0.htmlThe Reckoning (Post-apoctalyptic zombie mod. The modder working on this is a coding master, he's added working jeeps, helicopters and a cover system for AI):
http://forums.taleworlds.com/index.php/topic,271193.0.htmlSayazn (Low fantasy (No not magic, just in a world that isn't Calradia or the real world) gunpower mod, very very pain-stakenly done with all the features a line general would want. Also a unique and interesting lore):
http://forums.taleworlds.com/index.php/topic,291695.0.htmlCrusader-Way to Expiation (Mod that takes you into the 4th Crusade, much detail and work put into it. Been in production for years now but they intend to release Multiplayer this yeah):
http://forums.taleworlds.com/index.php/topic,161039.0.html