Core only makes it rough.
Have you considered Bard 7/Rogue/3/Arcane Trickster X? Your hit points, BAB, Skill Points, and Saves would thank you....
Spell selection would be very different, though. Not all bad mind you. You could wear armor, so Mage Armor wouldn't be necessary.
-Stuart
It depends. How long do you expect to play the character? Do you plan to raise his Dex more? If so, then it is fine to leave it where it is. If not, dropping your Dex won't hurt you at all - and an extra point of Con will give you a pile of hit points and a Fort save boost.
-Stuart
I remember seeing several things that were spellthief specific. I can't remember what they all are. In addition to the feats, I think that some of the prestige classes work well for spellthieves.
-Stuart
I created a Tinker class of my own (I'm not familiar with the WoW one). I based it loosely on the Bard. I altered their spell list, removed Bardic music and replaced it with bonus Item Creation feats, and gave them the ability to cannibalize magic items for XP that that they can then use to...
In a game I am playing in, I'm playing a Dwarf. I wanted to get away from the pseudo-Scottish stereotype, so I decided to base my interpretation of Dwarven culture very loosely on the Amish instead. Among other things, Dwarves tend to wear dark, wide-brimmed hats that have a chip of stone sewed...
Also, you might want to consider Ability Focus (Stunning Fist). Assuming you get a +6 Wis item, that would raise your Stunning Fist DC to 25ish.
-Stuart
I'd suggest taking a close look at all the tactical feats you can find and seeing if any of them strike a chord with you as far as fighting styles go. In general, if you make use of them regularly they tend to be really good. With a build like yours, you should be flexible enough to go in a...
I've written a bit about my reactions to it in my blog. In essence, I think it has a lot of cool stuff in it, but I am disappointed by some of the things that were left out.
Broken stuff? Some of the feats in there look a little too good. The multi-classing feats seem better than the ones in...
What about just subbing in 5 levels of Wizard spell progression for the Assassin's spell progression?
Then you can have something like:
Rogue 3/Fighter 1/Wizard 1/Assassin 8/Arcane Trickster 7
I'd also be tempted to see what you could do with Beguiler. You could possibly dispense with Rogue...
If Battle Sorcerer (Unearthed Arcana) is an option, that might not be bad. Low-level buffing spells (Shield, Enlarge Person, Expeditious Retreat, Blur, Mirror Image, Spider Climb, etc.) can be remarkably effective.
-Stuart