Mount & Blade: Warband and all DLC's are 75% off.
Damn you Steam. JUST TAKE MY MONEY ALREADY.
If you don't have any of the games, the bundle is a good choice. You get Warband and its two DLC/paid mods (that's essentially what NW and WFaS are), but you also get the original M&B, which may not be as good graphically, but has a whole slew of good mods that were not ported to Warband and have very very unique features.
Play as a necromancer, scavenging corpses and crafting items, then using those to help your hideously textured and modelled troops? Sure, Solid and Shade.
See Europe in the Napoleonic era, become a shameless social climber and be best bros with enemy officers to that degree you can actually ask them to do things for you even when you're at war? Order your troops to form big-ass squares because you're a fan of tableaus? Sure, Europe 1805.
Take part into a struggle between gangs, lawmen, US Army, ex-Confederates, Mexican Imperialists and Republicans, Comanches, Apaches and whoever happens to run into either of those at the wrong time, or just fuck off and go bounty hunting only to spend the money on prostitutes in Texas after the Civil War? Yep, grab that 1866.
Those are only the ones (except Custom Settlements, which is also awesome, but would take too long to describe) I played most. Warband mods tend to be a bit less unique feature-wise, but are far, far more pwetty and stable and sense-making, as far as I can apply that word to Warband.