Also from Sandstorm is a metamagic feat for +1 level that basically causes your fire spell to overcome all resistances, and the immunities of anything without the fire subtype (or something to that effect). I beleive it was called Searing Spell. With arcane thesis, you're applying that for free. It also makes Piercing Evocation (a feat I find worthless anyway, since it only actually helps if your spell was going to do 0-10 damage after resists anyway, and that's pretty cold comfort) and Energy Substitution not really needed.
Split Ray is normally awesome, but for scorching ray, you only get +4d6 damage from it, not say...a second disintigration ray.
Also look into an Empowered Spellshard (neck slot, but cheap enough to pay x2 for non-body) from Magic Item Compendium. 3/day as part of the casting action, the level 1-3 spell the shard is keyed to is empowered for free.
Residual Magic I heartily second, with lots of metamagic feats and spamming the same spell, it's like having double your highest 3 levels of spell slots.
Another option, if you're taking Energy Sub (fire) for energy admixture anyway: Acid Sheath from Spell Compendium (level 5 buff spell). It sheaths you in acid fire that damages anyone that attacks you. More importantly, it adds +1 damage per die of any acid fire spell you cast. Over the course of a fight, all those +1's can really add up.
It won't help for damage, but if you happen to pick up Weapon Focus (ranged touch spells), there's a feat in Complete Mage that lets you 3/day reroll a missed ranged touch spell. I don't think it's worth the 2 feats, but just putting that out there.