I'd focus on two of the following and do them well. Make sure your party knows your specialty. In addition, all Clerics should be prepared to issue relevant buffs at the start of raids as required.
1) Healing
2) Debuffing/CC (I group these together as both are forms of damage mitigation)
3) Melee DPS
um... THe only thing I can say here, that no one in their right mind, while putting together a High end raid, is going to say... "What we need now is a Melee Cleric!"
Dont get me wrong.. I'm All For Clerics that can melee.... But seriously.... That is the furthest thign form a Raid Focus I can think of. How bout some offensive Casting??? Harm, Searing Light, Cometfall, Blade barrier..... All highly effective in raids....
For Healing, you want maximise for mass cure spells (mass cure spells tend to be the best in most raids), plus you want a Superior Potency 6 scepter (or the Improved Devotion 8 set bonus), and at least the third tier of each of the Cleric Life Magic line and Cleric Wand/Scroll damage line. You'll also want twitch skills, (gained through leveling clerics in bad PUGs). In tough raids (e.g. Shroud Hard/Elite), you'll want significant resources too - for Elite I recommend 10 mana pots and 300 Heal scrolls, this cost should be shared by the party. Also, more SP is very helpful.
~CHOKE~
300 Heal Scrolls? 10 Mana Pots????? In a Shroud????? I havent come close to that kind of resource useage in VoD on Elite..... Let alone Shroud.... Thats First week of release type resource useage.... Unoptomized party useage levels..... not hard core Elite raiding resource useage.
For Debuffing and/or CC, you'll want a very high Spell Penetration rating - which usually means being pure cleric, and taking both Spell Penetration feats plus carrying a Spell Pen item. You'll also need a maxxed (or very close to max) Wisdom.
For melee DPS, you'll need a pretty dedicated battlecleric build (which will cause you to need to make sacrifices in the Spell Penetration and SP areas), and you'll want to make sure that your group wants you playing this role. (In fact, if I'm playing as Numot and want to run a Shroud group, if I see a group looking for a fighter type that has all the Clerics they want, I send them a tell and ask them if they want a cleric built for melee DPS - if I join a group that's after a Cleric, I don't usually play this role). You can be a very effective party member (3/4 as effective as a Barbarian at melee, 3/4 as effective as a traditional Cleric at healing and doing both simultaneously), but it isn't everyone's playstyle.
3/4th of a Barbarian? Really? I dont see how thats remotely posible.
Gearwise, the only true essential is the aforementioned Superior Devotion 6 or better item. Other good items are things that increase your survivability (Greater False Life; Minos Legens; +15 Balance item; Boots of the Innocent or Kardin's Eye).
OK, This Devotion thing is Driving me nuts.... THROW AWAY your "Devotion" Items and start carryign POTENCY on your clerics folks.... Superior Potency 6 Items are Everywhere..... and do the exact same as Superior Deviotion, Plu Increase damage on things liek Blade Barrier and Cometfall.
The feats, however, that no cleric should be without in current raids:
1) Maximize Spell
2) Quicken Spell (you may only seldom turn it on)
ACtually, I Seldom turn Quicken OFF