My longest campaign as GM was a homebrew system, so creatures didn't necessarily have D&D typical motivations.
For liches, generally they went senile, and clung to things that they liked doing in life. One lich was quite happy to have a cup of tea with the PCs, and teleported in on one other occasion to have a cup of tea.
One of the major bad girls was an immortal vampire-slayer. She had specifically not signed the Convenant of Immortals, and was allowed to interact with mortals (they left her out as they didn't want vampires gaining immortality). She went out of her way to prevent any vampires gaining immortality (normal vampires weren't immortal in any sense).
Deathwalker Rayburn, a vampire blinded by a laser-style attack by the immortal vampire-slayer. He managed to survive and later developed seer powers to see. His main motivation was survival and escaping from danger, as the vampire-slayer was on the lookout for him.
Various royals of the Empire. The motivations were power and there were lots of intrigues.
13 ancient (millions of years old) old ones, that were roughly equivalent to uberpowerful Mind Flayers. They had significant power within the psionic-linked-internet (unbeknownst to most of course). Once they realised it was possible, their motivation was to leave the planet and go to other life-bearing planets to have children and extend their species. Their species had ravaged all animal species for food, such that all PCs had instinctual extreme fear of them (and hence the reason why people were superstitious about the number 13.). Unfortunately, their offspring were too weak psionically to prey on the creatures that had evolved over millions of years to resist ... hence the need for a new planet.
Demons (synonymous with Devils really). A side motivation of the powerful demons was the Killing Game. You score points for killing people in as unpleasant and crafty a way as possible. Asmo and Baal were supposedly winning, but actually the number one was an entity known as the Gate. The Gate masquerades as heaven's gate, through which creatures go to heaven ... of course those lucky souls to get there just end up getting eaten (slowly) by the gate.
Ordinary demons played the Jugger, a game based on the movie The Jugger. The aim being to get a dog or goat's head to one side of the field. It was like league football, only far more unpleasant.
Yahkmot, the Destroyer. Yahkmot was in fact a program who's job was to erase the hard disk on which the simulation (and the game universe) was occurring. This result in the erasing of multiple stars etc .... The universe was slowly coming to an end (20 years), hopefully the PCs would figure out the maintenance portal exit point before then (not that we got that far).
