Problems
Links to some open problem collections:
Erdős Problems (Tao's site)
Erdős Problems (original)
Erdős Problems on Graphs
Open Problem Garden
Graph theory and Combinatorics (West)
Computational Geometry (Demaine, Mitchell, O'Rourke)
EGRES Open
SIGACT News Open Problem Columns (Gasarch)
Unsolved problems in combinatorial games (Nowakowski)
My questions on MathOverflow