Campaign or Chronicle Style
The most important consideration for character ideas is the campaign or chronicle style. A combat-oriented character is not going to fit in well, or have much to do, in a politics or court-based game. Likewise, a reserved, scholarly character will not work well in a one-shot, Pentex-style game. Checking in with the Storyteller is always a good idea, to see what she envisions as the style or tone for the chronicle.
Group Dynamics
Another important consideration is group dynamics. This is as important in "World of Darkness" games as it is in FRPG groups. If there are six players in a long-term chronicle and five are playing combat monsters, then a sixth combat-focused character is probably overkill. In that case, a more stealth, mystic, knowledge or influence-based character may be more helpful. A little comic relief -- goofy Malkavian, Ragabash or Nuwisha -- might not be out of place, either.
Sourcebooks
A great source of character ideas is the various sourcebooks published by White Wolf. In addition to the core rulebooks, the tribe, tradition, clan, kith and other sub-group specific books include some starting templates. Some of the other sourcebooks, such as the "Vampire: The Masquerade" books for Ghouls and Elders also include some templates. Most such templates fit within the clan and tradition stereotypes. Sometimes it can be fun to play a character who is the complete opposite of those types.
Historical Inspiration
History can be a source of inspiration, as well. Some characters can be based on historical figures such as Napoleon or Julius Caesar, or types such as samurai or Dominican friars. Others, especially in "Vampire" or "Mummy" chronicles, can actually be the historical figures themselves. Obviously, this method can take a bit of research for accuracy, but different gaming groups and concepts will seek different levels of accuracy.
Literary or Pop Culture Inspiration
An additional source of inspiration can be literary or pop culture sources. In both cases, it is better to use the source for loose inspiration, rather than create a clone. Playing a carbon copy of Lestat, for instance, is likely to elicit mockery rather than interest in a gaming troupe. Likewise, FRPGs, to use an analogy, have been saturated with Drizzt Do'Urden clones to the point that elves wielding two swords are generally met with derision and scorn. Even so, a Mage inspired by Shakespeare's Prospero or Neil Gaiman's Richard Mayhew could be interesting.