You will find detailed information about USA Visas in this Wikipedia article. Given your particular situation (Belgium citizen interested in working in the USA by no means of marriage), you may want to further research the H-1B and L1 visas. To my knowledge those two visas are the most common means to start working in the USA.
The H-1B classification is for professional-level jobs that require a minimum of a bachelor's degree in a specific academic field. In addition, the employee must have the degree or the equivalence of such a degree through education and experience. Before the H-1B petition can be filed with USCIS the employer must fill a "Labor Condition Application" (LCA) with the Department of Labor demonstrating that it is paying the required wage for this position in the geographic region where the job is located. The required wage for the position is the higher of the "actual wage" that is paid to other employees in this position or the "prevailing wage" which can be determined using nearly any source, including the employer's own wage survey.
L-1 Intracompany Transferee
The L-1 classification is for international transferees who have worked for a related organization abroad for at least one continuous year in the past three years and who will be coming to the United States to work in an executive or managerial (L-1A) or specialized knowledge capacity (L-1B).