| Tal-Findur |
I have played an evil character in a standard "lawful/good/neutral" campaign. You just have to get very specific with the character direction.
My character was a Cleric that had an intense desire to become a lich, so that he might "live forever." In his case, the only thing he truly cared about was knowledge. He wanted to be a permanent "library" to Kings and Gods alike. His "currency" (i.e. his treasure) was any tidbit of obscure information of a historical, magical, alchemical, etc. nature. He was lawful evil. The lawful part of him was able to swear not to hurt the other party members as they were -- to him -- a means to an end. They were able to help within the bounds of the party to keep him alive, just as he worked to keep them alive. He typically did this in somewhat strange ways. For example, he had the Knowledge Domain and the Undead Sub-Domain. One of the powers of the Undead sub-domain is the ability to cause someone to take on some of the characteristics of an undead creature with a touch-attack. What he would do is touch a party member, then use his Channel Negative Energy ability to "heal" the character. Somewhat creepy and unorthodox, but perfectly viable. As there were no lawful good-types in the party, they got used to his odd way of healing.
Also, the whole point of the campaign was that the world was invaded by an outside race of beings. My character wanted the world to go back to the way it was, so he had very strong reasons to work with people of all alignments to drive off the invaders.