I have 2 businesses.
First one is a civil engineering consulting firm. I worked for several large firms before I (with 2 other partners) started our own company. In 2003, our first full year in business for ourselves, we grossed $1.3 million. Far beyond our wildest dreams.
Second one is my own side project, an IT consulting firm. Build web sites, fix computers, set up networks, etc.
Started the first one because we got sick of seeing the owners of the firms we worked for drive new Porsche Turbos while we did all the work. So now we do the work and get to keep the money for ourselves. Plus we all work out of our homes and there are tons of other benefits. Only downside is that now I work about 90 hours/week. But it's for me, and that's a lot different than doing it for someone else!
Started the second one because lots of people kept asking me to do that kind of stuff for them and wanting to pay me for it. So for them to be able to deduct what they paid me from their businesses I had to start my own business to avoid IRS troubles.
I did lots of things before -
Paper route when I was a kid
6 years of retail management
6 months of selling cars
2 years as an electronics tech at a high-end audio manufacturer
4 years as a tech at a calibration lab
11 years as a civil engineer