here i would suggest a good start by looking and study what good logo has in commong at http://identityworks.com/
it's really inspiring to say at least, how even Visa or Kodak maintained their 'look' without even really made people go 'oh look, they've changed/omg who are they'

Look at their small case studies and as well 'Issues', so probably it'll spark some idea for you.
http://identityworks.com/issues/issues1.htm

Oh and yes, did i mention going to library and look for logo design book will help? Yes it does. I found one really good book talking about how they came out the identity for IBM and such. A very old and almost gone-case book, i'll see if i can dig the title back ,really nice 1.