Not sure if I'm answering the letter of your question, but hopefully the spirit of it.
I encourage the Mother Cyst feat from Libris Mortis for any "creative expansion of casting ability" builds.
This will give you a number of damage dealing spells, a sweet Scry spell, some make undead spells, a massive heroic stat boosting spell, 2 dominate spells and a "I've eradicated your soul from existance" spell. All really good with the Beguiler, as it's a "spontaniously cast from any spells I know" class.
The only problem is that those spells are kinda sorta evil, so it may affect your RPing & alignment, if those are important to you. Or, after becoming familiar with what they do, you can choose to use the spells selectively, a whole "Using evil things for a good purpose" if you can justify it to your DM and fellow players.
Arcane Disciple feat from Complete Divine is another great way to expand your spell list as well, adding divine spells to your arcane options.
As I said, not sure if this is what you're asking for, but there you go.
