If you have access to Complete Mage, may I recommend this build?
Human Cleric of Obad-Hai (domains Fire and Air)
1/ Power Attack, Scribe Scroll
3/ Fiery Blast (Complete Mage) -- keep a Fire spell prepared at your highest spell level, might require your top Domain slot.
6/ Craft Wondrous Item
. . .
9/ Summon Elemental (Complete Mage) -- keep a
summon monster spell in one of your top spell slots.
12/ Storm Bolt (Complete Mage) -- keep
chain lightning in your 6th level Domain slot.
15/ Quicken Spell -- Quickened Divine Power? Yes please!
18/ Heighten Spell (mainly to put Lightning or Fire spells at your top level if you want them there)
- - -
At this point, you've got some very nice crowd-control abilities, you can rain down fire and lightning at will, you can call an elemental servitor at will, you can mix it up in melee, and oh, you're also a full Cleric.
At level 7, you can blast a couple foes for 4d6 Fire damage at will (5 ft. radius burst, range 30 ft.). You are adequate in melee -- get yourself a light shield and a morningstar and mix it up.
Variation: drop Craft Wondrous Item; choose Craft Magic Arms & Armor at level 6 instead. Make magic weapons for your party of fighters, particularly +1 Bane arrows for all the worst foes that you expect to face.
Cheers, -- N