@2012: You say that your job is not challenging anymore. When this happens, there are normally 3 reasons i.e. (1) Work has become routine, (2) You have skills that are not utilised in execution of your duties (3) You are overqualified. The simple solution to this is to find a job where you are faced with highly specific situations and you can utilise all your skills. This applies only if you want to remain in employment. If you want to leave employment, I believe you've been given good advice along this thread.

The day I quit my last job, it felt as if the weight I'd been carrying around for a very long time had been lifted. I quit my job because my goals and those of my immediate superior became incompatible (he wanted to my career to stagnate, I wanted to overtake him). I loved my job but I didn't love doing it where I was doing it! Furthermore, it had become routine and I had competencies which the organisation did not recognise! By the time I was leaving, I had become very frustrated!

Don't wait too long to change jobs. Make a conscious decision to either seek other employment or go into business. The longer you stay, the more you waste!