It depends on what the OP wants. It soumds like he wants something more combat oriented. Beguiler is more of an intrigue style manipulator, while a rogue/wiz blend is more "I stab you in the back with my Scorching Ray" pew pew caster.
First rule of optimization is: thou shalt not lose more caster levels than required.
About your best builds here are:
Human
Rogue1/Wiz4/UnseenSeer2/StuffX
Spellthief1/Wiz4/UnseenSeer2/StuffX
Stuff can be more USS, Arcane Trickster, Spellwarped Sniper, and I've even seen Archmage in there for the Reach Spell High Arcana. I personally love USS, and recommend all 10 levels. The expanded learnings are awesome, and the persistant Nondetection is very nice.
As for feats, that depends on your level range. At low levels, Acid Splatter powered by Melt's Acid Arrow gives you an at will ranged touch attack that you can SA with, but at high levels it really loses its need as you get more and more spells per day. At high levels, I really like Persist Spell. Even without MM reducers, Persist + Hunters Eye and Cloud of Knives is pretty sexy for 8th level slots.
Otherwise, the usual rogue stuff. Darkstalker, Improved Initiative, etc.