I absolutely adore The Lesser Key of Solomon (free online here: http://www.sacred-texts.com/grim/lks/index.htm), a 17th century grimoire detailing "the ceremonial art of commanding spirits both good and evil."
The book is surprisingly readable and fun - it combines the absurdly bizarre statements and absurdly mundane. The spirit Agares takes the form of "a fair Old man riding upon a Crocodill, very mildly" and Gusion takes that of a Xenophilus (obviously). But their powers, while often dramatic and supernatural, also cover friendship counseling and help with geometry homework.
So I've compiled a quick and easy list of which demons to call to solve your daily problems (the parenthetical numbers indicate the order in which they appear in the book, for your convenience). Cross reference with the helpful details provided here: http://www.sacred-texts.com/grim/lks/lks05.htm
Do you need.....
Talk to Marbas (5), Gusion (11), Purson (20), Berith (28), or Asmoday (32)
Help with friends?
Try Amon (7), Barbatos (8), Botis (17), Glasya-Labolas (25), or Forneus (30)
Arithmetic? Ask Asmoday (32)
Mechanical engineering? Marbas (5)
Philosophy? Buer (10)
Astronomy? Morax (21)
Geometry? Asmoday (32)
English? Bune (26)
Demonology: not just for historical esoteric crazies anymore!