Here's an example of the technique I (sort of) described yesterday.
I wrote down these notes a few days after the first session. Roughly two-thirds of this material stayed valid through the last session.
Soern (the name is misspelled in the original document) would basically go wherever he heard their were magical items of interest to him, or interesting kinds of arcane power. Later on, he started collecting one of the magic item sets in the Magic Item Compendium, making him incredibly easy to motivate.
Sigrid (again, misspelled) dropped the justice motivator, partially because it was causing problems with the other characters, but mostly because it was more interesting to her player to be internally conflicted over her own motivations than to have the kind of clarity that the justice thing was best suited for. She later developed an attachment to one of the main NPCs in the campaign. That's something I didn't really mention before, but it turns out that a character who really cares about a particular NPC is incredibly easy (and fun) to motivate.
Rellik, on the other hand, is sort of a case study in wasted potential. I never really could figure out what was interesting to him, mostly because I was too busy with Sigrid and Blank to focus on him. Which I deeply regret.
Xerxed only showed up in the first session. He was retconned/replaced with Blank, because I thought he was too similar to Rellik and potentially destructive to the campaign, and because the person who played both of them thought being a pirate sounded fun. Thus was born Captain Blank, one of the best things to happen to that campaign.
Blank had a lot more handles than Xerxed, being interested in pirating and interaction as well as being cool, and he lacked the potential for psychopathic behavior. He later developed a personal vendetta against a nemesis, a subplot that was both very fun and somewhat underutilized.