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I'm playing a wizard who actually took widen spell...But I specifically wanted to play a wizard who could lay waste to multiple opponents with big area spells. Which I'm well aware is not the most optimum use for spells...But it sure can be fun.
He's 18th level, Wizard8, war wizard of Cormyr 5 Archmage 5. The cormyr's specialty is that they can spontaneously widen arcane spells times per day = to their CHA mod, and whenever they cast a widened spell, the area is doubled...IE 3 times as large as normal....that means 60' radius Delayed blast fireballs, and the mother of all 120' radius meteor swarms. He uses a Greater rod of Empowering and casts widened, empowered, meteor swarms, shaped to not injur allies and energy substituted to whatever energy type is necessary.
If we go against a single monster that can kill squishy types in a hit or 2, instead they get hit by an empowered energy drain, followed by quickened (via a lesser rod)empowered Ray of Enfeeblment.
You have to keep a hand free to cast a spell, which means you can only hold 1 metamagic rod at a time....But with 2 gloves of Storing, you can swap rods and use a quickening rod to cast secondary spells.
Back to the OP's question.
The good ones have pretty much been mentioned. Extend, Empower, quicken, rapid spell(for the summoner types). Higher levels, chain spell and split ray are real good too. Can you actually Chain a Greater dispel magic? I'd never considered it. When I play casters, I almost invariably take metamagic feats, and/or item creation feats. Other people in my group don't bother, but IMO are less powerful for it.
I think spontaneous casters shouldn't get free casting of metamagic spells....they are balanced perfectly well with being limited to 5' steps when they meta spells. They already receive more overall power and versatility from their metamagic feats as is. The PHB2 variant is fine, because it is limited.