Big fan of Dragonfire Adepts (Evil). Easy to play, never lose their utility and can be quite devastating if you decide to start stacking Metabreath feats, along with CON-focus with semi-decent HD for good health and plenty of UMD flexibility.
Why evil? Well because of Fivefold Breath of Tiamat of course. Far superior to the Discorporating Breath of Bahamut in every way.
But really, limiting yourself to one class/alignment is just...blechy. One has to spread their wings (metaphorical or literal, depending on your race) and branch out to experience everything there is to offer. I want to try a build based around the Spymaster prestige class in a primarily political based campaign (Eberron would be a good setting, would give me easy access to the Changeling race) too, but haven't had the opportunity.