One thing I rarely see in fantasy games is clerical lichs, which is odd since evil clerics have more power over the undead than magic-users tend to. One source for potentially awesome clerical lichs that fits well with the general anti-Catholicism of the Gothic is the idea of corrupt popes. Wikipedia happens to have a list of Sexual Active Popes right here that is chock full of interesting fellows ready for lichdom. Check out John XII, Benedict IX, and (of course) Alexander VI for inspiration.
Also worth looking at: antipopes.
(art by Andres Serrano)
(art by Jean-Jacques Grandville)