Beguiler would provide a few helpful spells (glancing over the list mage armor and charm person leap out at me). As well as provide a boost to will saves. Spellthief also gives a boost to will saves, but provides Steal Spell which may or may not be completely useful to you, and Sneak Attack.
There is also Scout. 1d6 of Skirmish is alright. 3 levels would provide a +1 to Fortitude saves and initiative checks, and uncanny dodge (which translates to Improved Uncanny Dodge), fast movement (+10ft to speed and +4 to jump is pretty good), trackless step (can't be tracked in a natural setting), and (1d6, +1 AC) Skirmish. However, Skirmish only affects attacks you make after moving at least 10ft, so a full attack with Skirmish is out unless you can find a way to move 10ft and still get a full attack.
I would probably go Beguiler 1 or Scout 3.
Depending on how long you are in your character (in terms of levels) a Beguiler/Rogue/Daggerspell Mage might not be out of the question. Taking practiced spellcaster mitigates the cost of levels, you would have to go cross class on Concentration though. Although, I don't know how well DSM and Beguiler work together.
Just my opinion. There's probably someone more qualified who'll offer a better one.