Dingleberry
First Post
Sorry, I should've been clearer: by "core" I meant just the PHB, and maybe the SRD variants. That said, I'll store away all the other suggestions for when I make a rogue cohort in my other campaign that uses more books.

That being said ...
... curious minds still want to know. How are you deciding to take that rogue of yours? Staight rogue? A little fighter? A little ranger? A bi of sorcerer?
If you're planning on making a martial character, I've found that multiclassing is a great way to go. (Unless your DM is using some weird house rule like favored classes.)
Essentially, dip into several different martial classes and you'll still be able to hit reliably. The more you focus on any one, the more you'll tend be useless in a significant percentage of fights. Rogues and rangers can suffer from that in particular, while fighters eventually run into the problem of not having any useful feats to take anymore.
-blarg
Aren't favored classes RAW?
I don't see how sorc or beguiler really mesh well with rogue. In the case of beguiler, you are probably off simply going pure beguiler instead (they get trapfinding already). Your sorc lv will likely be too low for the complementary draconic feats to be of any real use (between low DC, availability of energy resistance and SA won't apply to them either).
Even with only one Sorc level, the Draconic Breath weapon (as soon as 2nd in the chain) would give him access to at least 3 2d6 area effect attacks per day
Yes, my point is how 3 2d6 AoE effects can possibly be useful, even at 3rd lv?