Split Ray + Chain Spell + Arcane Thesis + Enervation = world of pain. 2d4 negative levels on all foes in a 30' radius area, no save, in a 7th level slot. Definitely worth the 3 feats. Plus Chain Spell is the most awesome metamagic feat there is. Go Archmage, pick up Arcane Reach as your first High Arcana, Chain Vampiric Touch on your enemies. Or if you're Epic, Chain Irresistible Dance (no save, no SR!).
Other awesome Metamagics:
- Quicken Spell is a lifesaver for those who prepare spells. Every high-level caster should have at least one Quickened Dimension Door prepared, just in case you meet a grappler/swallower.
- Sculpt Spell + Antimagic Field is so broken it makes me cry. Yeah, your CoDzilla now generates a donut-shaped Antimagic Field. His magic items and self-buffs work, the enemy's don't !
- Split Ray is veeery nice. Combine with Scorching Ray, for example... how many 4th-level spells allow you to deal 24d6 damage at CL 11? Or see above... Split Ray + Enervation is practically Energy Drain in a 6th-level spell slot.
- Chain Spell, the party's Über-buff! Chained Keen Edge, Chained Greater Magic Weapon, and much more! Über-debuff as well: Chain Dispel Magic, target the enemy fighter and all of his equipment! Chain Enervation, see above! Chain Ray of Exhaustion, the effect of Wave of Exhaustion in a 6th-level slot, followed by Chain Ray of Enfeeblement! Boo-yay!
- Permanent spell is a must have if you go Divine Metamagic. Permanent Greater Visage of the Deity, or Permanent Divine Power, anyone?
And don't forget to take Craft Rod to make your Metamagic Rods yourself, too, adding a bit of flexibility.
Metamagic means "Let's bone reality up the backside", even more than arcane magic already does. If you like this kind of games, it's simply awesome.