Armor: As far as other equipment goes, you want an r2 robe. You should upgrade its defense when you can, but it's not terribly important. You can also get rappelz gold by just fine with only minimally upgraded gloves/boots/helm/belt/etc. You'll rarely be hit, and when you do, a few points difference won't be that significant. It's good to do, but not essential. Enchanting your robes to +4 with defense cubes is a good idea, because enchanting boosts the MP regen bonus on the robe, whereas upgrading at the blacksmith doesn't. If you're choosing, enchant your robes rather than upgrade their level at the smith. NOTE however that the MP regen bonus you get from this is very small. If your rappelz gold is tight, this is *not* a priority. We're talking 2-3 extra MP while sitting, verses your existing 50-65 points per tick. Not a big deal.
Rings/Earring: Acquire two +4 dex rings. This should be the highest priority after your staff, and possibly even more important than your robe. Why dexterity? Because it increases your cast speed, and that's the single most important thing to a cleric. You'll find out why below.
Cards: the most important one to have is 1 or +2/+3 heal. Why Heal and not buff cards? Because a heal card further reduces your cast time for heal, and heal is your single most important skill of course. It's expensive, though... I bought 5 heal cards at 800k each and broke four of them trying to make +2. I'm still just using a single +1 heal card. Buff cards sell for around 1 million rupees for clerics - I don't have any. I could buy one or two, but I just won't at those prices. I don't blame people for the prices of them - it's just not worth that price for me personally. Kahunas can also buff, and their cards are half the price of cleric cards. I generally rely on kahunas for higher level buffs. If a kahuna doesn't have higher buffs, or there's not one in party, I give people lvl5 buffs and we all still get by fine with that at high levels. Remember, also, that with the release of the new jobs soon, there will be much higher level buffs around from many of the new subclasses. So don't fret too much about getting your buffs high level. If you can, do so, but it's not that important. As far as priorities go, though, you should prioritize: Heal, Bless Weapon, Mental Amplify (because this helps your heals also - matk), Bless Armor (helps the group take less damage).