Advice to Research Students: Some tips for solving problems in number theory, collected by the Cardiff University group.
L-functions and Random Matrix Theory: Conjectures and open problems concerning L-functions, focussing on the areas in which there has been recent progress using results from Random Matrix Theory. Maintained at AIM.
Mathematician's Secret Room: Unsolved problems in Number Theory. English and Japanese text by Hisanori Mishima.
Number Theory Conjectures: A collection of easily stated conjectures which are still open. Each conjecture is stated along with a collection of references.
Open Problems: Some questions compiled by Jon Perry.
Seva Lev's Problem Page: A collection of research problems.
Unsolved Problems and Conjectures: Regarding equal sums of like powers, compiled by Chen Shuwen.
Unsolved Problems and Rewards: By Clark Kimberling. Offers prizes for solutions of some problems in number theory.