Beguiler (PHBII) is completely what you are looking for - it is a spellcaster who gets up to 9th level spells, wears light armor, and has a ton of skill points (and rogue-skills). The Beguiler casts spontaneously from a set list (Int-based caster). The spell list is mostly Enchantment and Illusion with a dash of Divination, but it includes some other spells that are useful to sneaky/clever characters.
The big weakness for the Beguiler is that they have no direct damage spells (other than a few that do nonlethal damage). They do get UMD, though, so they can pick up wands if they want.
-Stuart