Class crossing question

[Garlyle]

Enkidoh covered the basics. The cross-class skills available to you as PLD are limited and generally optional. None of these skills are "mandatory" in the way certain other classes at high level play will find them (Warrior, for instance, needs Gladiator's Provoke to do certain fights!), although I certainly wouldn't neglect Foresight. Seriously, level 2 skill. They're just nice advantages to have.

My personal selection of five is Protect, Foresight, Stoneskin, Bloodbath, and Mercy Stroke

Protect (listed first) helps ensure you always have it in party content even if your healer doesn't.
Foresight is a skill learned at Marauder level 2 (so there's no excuse, seriously) and it's a free awesome defensive cooldown.
Stoneskin will require significant CNJ levelling, but is well worth it; if you cast it while bosses are occupied with their own casts, you can stave off a lot of extra damage.
Bloodbath does generate a tiny bit of extra aggro due to the healing you're generating, and hey, free healing is nice.
Mercy Stroke is not much, but a free hit for extra damage off your GCD is nice for helping burst things down. The healing's just a bonus if the stars align because realistically it's super hard to time.

Fracture and Cure just don't hold up, and Skull Sunder is straight up a less useful (to you) version of Savage Blade, so yeah. Not much competition.