I've got a few favorites.
1. Holy Liberator. It's easily accessible to bards, monks, clerics, rogues, ex-paladins--anyone with Diplomacy as a class skill. And since it only requires 5 ranks of Diplomacy, it's really easy to get into if you multiclass with one of the above classes. And the pre-req feat (Iron Will) is actually useful.
From a powergamer perspective, the abilities are great: Divine Grace, Smite, Turn Undead (giving access to Divine feats), resistance to enchantment, celestial companion (including the possibility of a winged celestial horse) spells (including Bless Weapon). All with a fighter's BAB.
From a roleplaying perspective, the idea of a divinely-inspired freedom fighter is very inspiring.
2. Templar. From a powergame perspective, this Prc just rocks. It gives Weapon Specialization at first level. Mettle and a successful save takes care of pesky Inflict, Harm, Poison, and most Death spells. Damage reduction, bonus feats, and spells are icing on a very powerful cake. Too bad that if you pay attention to the RP requirements (defending a temple), you'll have a hard time justifying an adventurer's lifestyle.
3. Shadowdancer. From a roleplaying perspective, this class is just plain cool. Very interesting abilities. My next character is going to be a shadowdancer. Too bad it's not very powerful in combat.
4. Duelist. If my next character isn't a Shadowdancer it'll be a duelist. Bonus: the feat pre-reqs are the same. Precise Strike effectively turns your rapier into a greatsword (with a better crit range). Deflect Arrows is fun. Play a monk/duelist, take Leadership as your 6th level feat, and get a mage cohort to cast Mage Armor and Int and Wis-boosting spells on you, and you'll be an AC king. Good times.
-z
