LX--can I call you LX?--made a very valid point. Every name has been used before. You can't be too picky about these sort of things. Honestly, LX's suggestion was perfectly fine. Not everyone sees the name O'Donohue and says "Oh man! What a rip-off of Becky O'Donohue from American Idol." People have to be looking for faults in such a name to actually find them.
Don't get nit-picky about who shares the same/similar names with those you choose. Chances are, the people reading won't give half a damn if Donovan is the name of a character from Darkstalkers. Most people will look at it, recognize that it's a somewhat common name, and move on.