I usually like to play a character that is a variation on a theme (elven paladin who embodies their diety in a druidic more than King Arthur sense.) or as a case study in conflicting tendencies (The happy bard that *wants* to see the good in everything, even 'monsters' while needing evil to add drama to his/her tales or the sorcerer hiding his talent out of fear by trying to pass off as a ranger).

I'll RP good or evil, but since RPing evil is so hard to do well and not get lambasted OOC for being a jerk, I tend to play good unless I know the others in the party.