I'm currently going through a period of similar introspection and want to share my thoughts. My introspection has been brought on not by dissatisfaction with my job; quite the opposite. I am an IT consultant for a large firm. I get paid very well and the work is challenging. My coworkers are excellent--competent, friendly--and even my management is essentially made up of good people. I'm 26 and have achieved what many try to achieve in the IT field for their entire careers.
I've become too satisfied with my job. It took me a while to realize it, but while reading Kafka recently I came across the concept that struggle is what gives meaning to our lives (obviously nothing new but poignant for me at the time). I realized that I could look back on the past 2 years of my life and remember almost nothing but meaningless crap. In the end, it's not your job satisfaction that makes your life meaningful, it's the struggle to achieve something that you care about.
Most people delude themselves that their career-related struggle is to reach a certain point in their career where they can be happy. But I'm telling you, I'm at that level, and once you get there "coasting" is no fun. It's meaningless, and it leads to boredom and depression.
So what am I doing about it? I'm rediscovering what I care about. I set out on a mission about 6 months ago to figure out what I believed in and what I could do to help. I've been reading non-stop, I've been networking with useful people and I've been trying to figure out how I could fashion a career that would allow me to be passionate about the end results, rather than "job satisfaction". Most likely I'm going to go into project management with a green developer, building environmentally conscious homes for middle-income families. After a while there, I may develop software for local artisans and farmers to help them bring products to market.
A critical point--you don't need as much money as you think you do. Two reasonable incomes go a long way in many locations and devoting your time to something you love will reap much larger rewards than the monetary ones you left behind.