Holy Bolt
Description: Weak "Holy" elemental attack spell.
Requirements: Level 5, I think.
Required for: Level 10 for Holy Blast.

Note: Weak skill, but with the added MATK of any rare weapon, it is quite useful for slaying bosses at long range. Unless you plan to get Holy Blast, put only 1 skill point on this. Currenlty, rings/amulets of elemental damage also raise MATK, as well as ATK, by 10 points each. Better for maul users due to aded MATK of rare mauls.

Holy Blast
Description: Theoretical: Similarly weak "Holy" elemental Blast spell, similar to Lightning blast for mages. I have not learned and cannot verify.
Requirements: Level 25, Holy Bolt level 10.
Required for: None known.

Smash
Description: Three physical strikes. Good against a single opponent.
Requirements: Level 10, I think.
Required for: None known.

Notes: Quite similar to the warrior skills, all of the cleric's physical skills are useful for dealing damage quickly to either a single or multiple target(s).
Update: Smash is very effective even at level 1, and can be used to take down strong opponents quickly, but the cooldown prevents rapid fire usage. Best for hit and run on bosses, also can be combined/chained with sweep to deal massive damage very quickly. All physical skills should be learned for maximum fighting effectiveness, but leveling them up beyond 1 is not necessary.

Rush
Description: A physical line attack, like Hyperslash. Good for multiple targets in a close group.
Requirements: Level 15.
Required for: None known.

Sweep
Description: A multiple spinning strike attack against a large group. Deals 4-5 hits at full strength to all opponents next to the user. Excellent for dealing with large groups or strong enemies.
Requirements: Level 40.
Required for: None known.