Tell me about yourself?
This is probably the most asked question in an interview. It breaks the ice and gets you to talk about something you should be fairly comfortable with. Have something prepared that doesn't sound rehearsed. It's not about you telling your life story and quite frankly the interviewer just isn't interested. Unless asked to do so, stick to your education, career and current situation.
Why are you looking for another job (or why did you leave your previous job)?
On the surface this appears to be a simple question, yet it is easy to slip. I would suggest not mentioning remuneration at this stage as you may come across as totally mercenary. If you are currently in employment you can say it's about developing your career and yourself as an individual
What do you know about this organization?
Do your homework prior to the interview. Doing the background work will help you stand out. Find out who the main players are, have they been in the news recently? You only need to have a solid understanding of the company as a whole.
Why do you want this job?
This questions typically follows on from the previous one. Here is where your research will come in handy. You may want to say that you want to work for a company that is x, y, z, (market leader, innovator, provides a vital service, whatever it may be.
Who are our main competitors?
This shows you really understand the industry and the main players. Think about a few and say how you think they compare; similarities, differences. This is a good chance to highlight what you think are the company's key strengths.