You are definitely not alone when it comes to finding it difficult to answer this question! So many people find it extremely hard to talk about themselves and they spend hours before the interview trying to work out what it is they are actually supposed to say. Generally there are no right and wrong answers as each employer is looking for something different. However, there are ways you can calm yourself down so that you do not get tongue tied.

Firstly, take deep, long breaths before you go into the interview. The best way to get through it is to act like it is more a meeting of friends (though a formal one if that makes sense!). The more intimidated you are, the more nervous you will be so if you look at the interview in a positive light you will get through it with hardly any problems. As for what to actually say to the question, just a general overview of your main accomplishments and your employment goals should be enough. Just follow your instincts and try to relax as much as possible.

 This can be a tricky question. Its best to consider your answer carefully before you go in because you can bet on them asking it. Luckily, the more interviews you have the easier it will become.
If you are female and of child bearing age, its probably not best to tell a potential employer that you want to take a few years off for a family soon. Also, be careful of admitting you really want to be jetting off around the word with a backpack rather than sat behind an office desk. Although skydiving makes you sound like a really interesting person, to a potential employer this could spell time off for breaks and strains! However......this is a great oppertunity to sell your interpersonal skills and creativity.

Good things to mention; ( its kind of nice if you can find someting a little different to the norm to add here. Dont be shy to admit to belly/ salsa dancing, or owning a myspace!)

How cheerful you are, your extended friend network.
Sports, (even if the last time you were on the football/ hockey/ netball team was at school its time to rekindle your passion for the interview!)
The arts,
Music,
reading,
IT ( especially programmes you have knowkledge of that are not specifically required for your role or you have not yet had an oppertunity to disclose)
holiday travel,
An instance of team playing ( groups or societies)
An instance of leadersip ( even looking after siblings!)
Work related voulenteer work

Not so good things to mention;

Extreme sports
Desire to take a gap year
Voulenteer work which could mess with you doing said job
The want to start a family ( If female!)
Love of late night partying at the local strip club
That you are a smoker ( unless they ask!smokers take more, and longer breaks!)
Gambling ie. horses or dogs (an impulsive risk taker)
boxing or aggresive sports ( temper temper)
That you intened to appear on reality tv. This, i strongly suspect, would be a major turn off to a potential employer ;-)
That you were nicked the night before

I hope I have helped :-)