This build is a variation of builds I have seen by other builders, including Darshue, Falconhurst, oli84, XyberKnight, among others. Still, I didn't see any Blackguard versions in the index, so I figured I might as well post it.
1 Power Attack, Cleave 3 Still Spell 6 Spell Penetration 9 Greater Spell Penetration 12 Weapon Focus: Scimitar 15 Great Cleave 18 Improved Crit: Scimitar 21 Epic Weapon Focus 24 Overwhelming Critical 27 Devastating Critical 30 Epic Spell Penetration 33 Auto Still-Spell I 36 Auto-Still Spell II 39 Auto-Still Spell III, Sorc: Epic Warding
Note: If you don't want the Spell Penetration feats, feel free to take Spell Focus or Metamagic feats instead. I know some people like their Sorcerers to be able to cast Maxed or Empowered IGMS, so feel free to take whatever you want.