Since Clerics have a longer list of spells to choose from than wizards, their options are wider and their spells should be "weaker." Adding in all the other abilities of clerics, it shouldn't be a surprise that they are a powerful class in and of themselves. In fact, if you gave clerics the attack progression of wizards, it wouldn't make them useless, in my opinion.
But that's not the point of this post.
On average, clerics have about 20 spells to choose from at each level (although at 9th level, they have only 11 options). The most spells of a given level that a wizard can "know" is 9... and this is when they reach mastery levels. At 1st level, a cleric knows 25 1st-level and 12 0-level spells!
That means, everytime a 3rd party company introduces a new cleric spell, clerics just get more powerful. More options are added. More spells that clerics may choose at each level. More. More.
It's insane how powerful a cleric can become with just four new books from Green Ronin, Mystic Eye, Paradigm, and Bob's House of Books. And if one of those is the pocket grimoire, clerics are now the most powerful class in the game... perhaps 50% more powerful than a rogue or wizard.
That's just insane.
And that doesn't include feats that allow the cleric to trade out unless turn undead attempts.
Am I painting a vivid enough picture for everyone? Do I need to continue selling this theory?
Because I'd like to move on to the solution, which is really pretty simple.
If a player wants to add a new divine spell to his list of "known" spells, the DM must select a comparable spell to be removed. Just getting rid of magic stone to add barrels of blood is NOT an option in terms of balancing the spell selection. DMs need to look at the effect and see what spell is most similar to it. If the new spell causes the target to incur a penalty to attack rolls, bane or doom should be removed from the list.
And so on.
I think that's about all I need to say on the subject. Next, I tackle conjuration magic.
Speak of which, clerics should not be summoning monsters, either.
Those spells need to go.
That is all.