There are a few concepts that you would do well to familiarize yourself with. They arose in the evolution of competitive cleric building. They are:
- Fighting better than a fighter
- Using turn undead
- Doing "un-clerical" things.
I could literally write pages and pages about each, but these are the main concepts you need to get comfortable with.
Fighting really well: a cleric with the right domains (say, Strength and War) can fight better than a fighter of equal level. He's already got the same armor proficiencies; War gives him the ability to keep up with a weapon, and he has spells which more than make up for his slightly lesser hit dice. As he gains levels, his spells get more and more powerful, faster than a fighter's feats do.
Using turn undead: Most of the time, you aren't fighting against undead. You'd think that would mean your turn undead powers would be wasted, but there you are dead wrong: divine feats have been made for this purpose. Divine Spell Power increases your caster level, whereas Divine Metamagic allows you to apply metamagic without raising a spell's effective level. Both can be broken if you use them in certain ways, so some DMs frown upon them. You should be aware that they are very powerful options, so consider them.
Filling other shoes: with certain utility spells and/or domain powers, clerics can temporarily gain trapfinding, make high skill checks, cast arcane spells, and so forth. You should be aware that it's possible to do things like build a cleric that sneaks around, steals things, and bluffs like a Rogue, or one that can use wands of fireball more or less like a mage can. We've already covered that a cleric can be a front-line tank like a fighter can.
You can do what you want with the class; I'm just trying to show you that there are many possibilities.