Suppose:

• I am a 'problem-solver' rather than a 'theory-builder'
• I am an undergraduate student
• I have a passion for solving mathematical problems
• The homework I get is not satisfying (in the sense that the problems are computing-problems rather than problems that require creative thinking), and I get far too little homework

Where can I find interesting problems (that require creative thinking) if I want to have fun solving mathematical problems and to practice problem-solving? Are there lists/books of such problems?

Furthermore, suppose I want to know how it is to do research.

Are there lists of the kind "open problems which can be understood by undergraduates". I guess these open problems should be in the fields of "discrete mathematics/combinatorics" and "graph theory".

I only found: http://dimacs.rutgers.edu/~hochberg/undopen/