You may want to see if your DM will let you use the Shadowcraft Mage with the change of Race: Gnome to Special: Must be a member in a Shadowcraft Cabal as suggested by the book.
Beguiler 5/Mindbender 1/Beguiler +2/Shadowcraft Mage 5/Shadow Adept 6/Nightmare Spinner 1 would be a powerful build.
Take the pre-reqs for Shadowcraft + Heighten + Shadow Weave, you may also want to consider the feat from Complete Mage that lets spontaneous casters make actual use of metamagic by not increasing the casting time on it.
Depends on what you want though.
Also, a note, if you do take a level of wizard, make him a focused specialist conjurer (drop illusion, enchantment and evocation) and take the specialist variant presented in PHB II to get Abrupt Jaunt -- otherwise known as "OHSHI- BYE!" -- feature instead of a familiar.