A cleric may prepare and cast any spell on the cleric spell list, provided that he can cast spells of that level, but he must choose which spells to prepare during his daily meditation.[/spoiler]
[spoiler]Benefit: You can use two spell slots of the same level to cast a spell you know that is one level higher. For example, a sorcerer with this feat can expend two 2nd-level spell slots to cast any 3rd-level spell he knows.[/spoiler]
The first part is from the SRD, and the second part is from the feat Versatile Spellcaster.
So let's see how we can abuse this:
Clerics can cast any spell from their spell list, as long as they have a cleric slot to cast it from.
This is fine, because otherwise you could get all Cleric spells by dipping one level, which would be crazy.
However, let's take a look at that Versatile Spellcaster; it allows you to sacrifice 2 spell slots to cast one spell you know one level higher.
It never says it has to come from the class whose spell slots you're burning.
So a Warmage 19/Cleric 1 (for example) with Versatile Spellcaster and Heighten Spell could cast every single spell of the cleric spell list, as long as your willing to sacrifice 2 spell slots for it.
Same could be done for a dip in Druid. In fact, since the spells you would be casting would still be divine spells, you could argue for the following build: Warmage 1/Cleric 1/ Druid 1/ Warmage 3/ Prestige Paladin 1 (advancing Warmage)/ Prestige Bard 1/ Prestige Ranger 1/ Warmage+11.
With the following feats (in order): 1st. Versatile Spellcaster, Track, Endurance. 3rd. Mounted Combat. 6th.Precise Shot (or TWF). 9th. SotAO. Whatever from this point on.
You get: 9th level Warmage, 9th level Cleric, 9th level Druid, 6th level Bard, 4th level Paladin, 4th level Ranger, and 8th level Wizard spells.
Looks nice, doesn't it?
If this doesn't work, please point out, as precisely as possible, why it does not.