Uses for high caster levels?

[Zombimode]

There are some ways to gain higher then normal caster levels. A Bead of Karma for instance, and I'm thinking of a Persisted Consumptive Field. There are others of course.

The question is: what to do with higher caster levels? What spells do really profit from it? Most damage spells cap out relatively early, so thats not really efficient.

[peacenlove]

Undispellable buffs.
Maw of chaos from spell compendium.

[Dread_Head]

Holy Word becomes really powerful with a high CL

[Yuki Akuma]

Spells that last for hours per level are good to cast in conjunction with artificially raised caster levels. Artificially inflated caster levels are also nice to have in case you need to get a spell through someone's spell resistance, or if you want to make a spell as hard as possible to dispel.

[TuggyNE]

Reserves of Strength, if you want to be all cheesy about it.

Popping AMFs with disjunction.

[Chronos]

It also depends on what you mean by "high caster levels". CL 20 isn't high for a 20th-level character, but it is high if you can get that at, say, level 10. And there are a lot of spells that don't cap out until 18 or 20, and capping them early can be useful.