I think we all have our inner demons. Fear, madness, depression, anger and such. It sometimes seems the great men of the world have the biggest demons. Some hide theirs well.
I would have to say my two is Doubt and Weariness. Doubt plagues me the most, and seems to drive me to near madness at times. I fight it though, and just about everything I do is done to prove that demon wrong. Which of course causes the demon Weariness to rear its ugly head. A lethargy settles over me, and I don’t ever want to do anything when it has control of me. It is like depression I think, in its strength, but sister to doubt in its weakness.
What demons are behind the crafty and cunning minds of those here at the SDMB? What drives you and pushes you forward, what great forces tear at you night and day, driving you towards your genius? What demons haunt you?
Fear drives me…fear of not living up to a noble purpose in life, fear of succumbing to mania or depression, fear of death, fear of intimate relationships, fear of fear, fear of posting nonsense, fear of eating too much black licorice(see previous fear)…yet I perservere.
I’m driven by Romanticism and hounded by Cynicism, lifted by Optimism and drawn down again by Pessimism…all borne upon the shoulders of the shadowed Past. I am Balance.
I am also Sleep-Deprived, which surely cannot affect the quality of my postings…did you really think this out before starting the thread? 
I’m dreadfully afraid of insufficiency, of not being good enough in general for anything… not being able to accomplish what i want and of being left alone and of making people not want to be around me. i fear that people are politely lying when they compliment me and i often have a hard time trusting compliments. i fear that i’m not attractive, that my body can’t attract others. i fear that when i choose to express myself artistically or politically that it’s merely dilletantish and incompetent.
I don’t consider my demons as driving me, more like weighing me down. I guess mine would have to be anger, frustration, and homosexuality. It’s not like being gay is a demon, it’s just that when all of your friends and all your peers talk like they’re homophobic, it feels that way.
The fear of deceiving myself. The fear that I’ll sink slowly into a mundane life, settling for not very much, and just bumble along. The thought that this is it plagues me. As a happy atheist, I am comfortable with the idea that when we die poof we’re gone, but the consequence of such a belief mean that it’s incredibly important to make the most of right now because this second, this minute, this day will never happen again. I’m scared to miss things, scared I’ll never have children (my path to immortality ;)), scared I won’t contribute.
Sometimes this paralyses me, sometimes it drives me.
I, too fear not being good enough. I fear that I’ll fail in everything. Brief, fiery, but ultimately pathetic enthusiasms drive me - knowledge of my incapability and lack of mental and moral fibre hounds me. Giving up because I know I’m useless is my Demon.
I am driven by Mojo the Helper Monkey.
Wendy.
The silly answers have already started, but I wanted to say that I am powered by a small Maxwell’s demon. He keeps the hot side hot and the cold side cold.
K’Z’K.
Damn! Someone beat me to it!
I’d have to say duality is my demon.
I never see an upside without searching for a downside.
Of course, I also never experience a downside without reflecting on what could be the upside.
It’s enough to drive you to distraction.
Vanity of vanities, all is vanity.
Doubt. Low self-worth. Loathing of my own hypocrisy, and fear that someone will call me on it.
Sometimes I feel that everything I do is calculated and comes from layer upon layer of artifice, sly motivations, and dishonest intentions. Thank god none of YOU have noticed.
Mainly fear of being insufficient and fear of not being ‘equal’ to others. Unfortunately for me being ‘equal’ doesn’t mean on par with normal people it means being equal to the best. A bit of selfish perfectionism I guess. I’m an egomaniac with a confidence problem. Fairness is also a big issue with me - when things aren’t fair (or more specifically unjust) I get really upset.
Cranky summed up mine better than I would have.
Valraukar, or spirits of flame.
The realization that I have a thousand different masks I have to wear because I can only be my true self around 3 people at most. There are only 3 people that I can trust with who I am right now. There are some that know a great deal, but not all, and most know very little of how I think and why I do what I do.
Some masks are necessary, however, I do not like feeling that I go through my life as an actor playing a part.
I have to lie to do what I want to do, in secret, behind closed doors. There’s no real scandal in what I do, no big secrecy or conspiracy…I just can’t be honest with myself quite yet. I think that someday (hopefully soon) I will be able to be honest with myself, instead of just 3 people.
I’ll take my demon over a Balrog any day of the week.
I hear those whips really hurt.