|There is only today, and today I take what I need.
|— Ultimate Campaign, page 136
Chaotic evil characters are typically out to get whatever they want at that moment, with no consideration of their acts' effects on others. However, some devote themselves to the spread of more insidious evil. Chaotic evil can be charming and urbane but brooks no resistance to its goals except those imposed by a stronger force. Even then, it schemes to remove the obstruction without any personal sacrifice. Typically, chaotic evil entities can only be kept in line by a stronger force above them. Thus, societies of chaotic evil creatures like drow and gnolls tend to be brutal, ruled by the most powerful individual. Religion is often a uniting factor with this alignment; what force is more powerful than a god?
Rovagug is typical of chaotic evil deities. The Rough Beast is a force of utter destruction, his only whim being one of constant annihilation.1 The other major chaotic evil deity is Lamashtu, the Mother of Monsters, who is also utterly fickle in her evil.2
Demons are one of the extraplanar incarnations of chaotic evil. They derive sadistic joy from acts of cruel destruction, reveling in mortal pain and misery. Before the demons, the ancient and utterly alien qlippoth dwelt in the Outer Rifts long before the existence of mortal life.3
For additional as-yet unincorporated sources about this subject, see the Meta page.