Have a tough time thinking of questions to ask at the end of an interview?  First couple times I had interviews, I was often too nervous to think of decent questions on the fly.  You should be prepared with some generic questions if that is the case.
Why is this position available?
Is this a new position?  How long has this position existed?
How many people have held this position in the last two years?
Who would be my supervisor?  To whom would I report?
Whom will I supervise?
With whom will I be working most closely?
What do you like about working for this company?
What are the current plans for expansion or cutbacks?
What kind of turnover rate does the company have?
How financially sound is this company?
What projects and assignments will I be working on?
What happened to the person that held this position before?  Was he promoted or fired?
What is this company's culture?  (Ex: Is it rigid and formal or relaxed and flexible?)
What are the current problems facing the company (or my department)?
What do you like the most about working for this company?  The least?
What is the philosophy of the company?
What do you consider to be the company's strengths and weaknesses?
What are the company's long and short term goals?
Describe the work environment.
What attracted you (the interviewer) to this organization?
Why do you enjoy working for this company?
Describe the typical responsibilities of the position.
What are the most challenging aspects of the position?
Describe the opportunities for training and professional development.
Will I receive any formal training?
What is the company's promotional policy?
Are there opportunities for advancement within the organization?
When can I expect to hear from you?
Check out College Grad Resource site for more questions tailored to different members of the company you're interviewing for.