I'm a big fan of greater/ultimate mercy (Greater is good, Ultimate mostly for flavour). You could check out some Paladin specific feats HERE (not a complete list, but there are some fun things on there).
For more general advice, Improved Critical will likely add a lot of damage when smiting (you could follow it up with Bull Rush Strike), and Lunge is always good on a melee character.
Following-Step, and Step-Up-And-Strike could be fun.
You could take Deadly Aim for when you need range if you have nothing else to add to melee.
definitely the step up line is excellent. you're cha based, so if you've invested in intimidate at all, cornugon smash is almost a no brainer. dazzling display becomes an option too, since you've got the prereq already. just ideas
Unsanctioned Knowledge can be pretty cool. It takes 13 INT, but that's not too tough at higher levels unless you dumped INT. Heroism, Good Hope, or Dance of a Hundred Cuts are all nice morale buffs. Mirror Image and Displacement are pretty fantastic. Dimension Door opens up Dimensional Dervish if you can use Retraining rules for the feats.
Another option would be to multiclass into powerful options, but that depends a lot on build details. One level of Celestial Bloodline Bloodrager and one Extra Rage grants plenty of holy Rage with a Furious weapon. Three levels of Horizon Walker opens up Dimensional Dervish. Two levels of Ninja opens up a CHA-based Ki Pool and Extra Ki, granting extra Ki attacks (works just fine with greatword) and possibly Shadow Clone.