The Telepathy from Mindbender is not something that fits well into most campaigns.
Therefore I adapted the Gnomish Mindbender/Shadowcraft Mage Build to make a Gnomish Shadowcrafter/Shadowcraft Mage Build.
You can substitute Shadowcrafter (Und 43) levels with Rainbow Servant (CDiv), but the I think verdict is out on if you gain the entire Good domain as a beguiler.
Build 1:
Beguiler 5/Shadowcrafter (Und 43) 1/Beguiler 2/Shadowcraft Mage 5 (RoS 120)
Requirements for Shadowcrafter: Spell Focus(Illusion), Greater Spell Focus(Illusion), 3rd level or higher shadow spell, Disguise 4 ranks
Requirements for Shadowcraft Mage: Race: Gnome. Skills: Bluff 4 ranks, Hide 4 ranks. Feats: Spell Focus (illusion). Spells: Able to cast at least three illusion spells, including at least one shadow spell of 4th level or higher.
Suggested Feat: Penumbra Bloodline (at level 3 or 6 or 9), this unlocks 5 extra Shadow/Ethereal themed spells for your Beguiler spell list (Darkness, Evard's Black Tentacles, Shadow Evocation, Plane shift, Greater Shadow Evocation) at the exchange of the loss of your Dancing Lights Spell as well as all Light Evocations (0:Dancing Lights, Flare, Light; 1st: Guiding Light, Lantern Light, Light of Lunia, Light of Mercuria, Light of Venya, Luminous Gaze; 2nd: City Lights, Continual Flames, Rainbow Beam; 3rd: Daylight, Glowing Orb, Rainbow Blast, Wall of Light; 4th:Blistering Radiance; 6th: Ray of Light; 7th: Radiant Assault; 8th:Sunburst) and these other spells (if you somehow gained the ability to cast them: Blinding Breath, Breath Flare, Lucent Lance. I think it is worth it as it gives you early access to Shadow Evocation. It is explainable to take at level 6 or level 9 as you are entering a Shadow class.
This is the build I am getting ready to play.
Build 2 (Slower but higher advanced learning):
Beguiler 5/Shadowcrafter (Und 43) 1/Beguiler 1/Shadowcrafter 1/Shadowcraft Mage 5 (RoS 120)
If you take 2 levels of shadowcrafter before shadowcraft mage, you could push Advanced learning 2 so far ahead that it would net you level 7 or lower spells instead of level 4 or lower. It also has the benefit of pushing Advanced Learning 3 to level 18, which allows you to learn a level 9 spell. Which essentially means, instead of Shadow Conjuration, you can get Greater Shadow Conjuration at level 14 then you can get Shades at level 18. The downside of taking an additional shadowcrafter level is that you lose the Cloaked Casting (+2 DC) you would have gotten at level 20.