Unsolved Problems and Conjectures - http://euler.free.fr/eslp/unsolve.htm Regarding equal sums of like powers, compiled by Chen Shuwen.
Unsolved Problems and Rewards - http://faculty.evansville.edu/ck6/integer/unsolved.html By Clark Kimberling. Offers prizes for solutions of some problems in number theory.
L-functions and Random Matrix Theory - http://www.aimath.org/WWN/lrmt/ 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.
Number Theory Conjectures - http://www.math.umbc.edu/~campbell/Math413Fall98/Conjectures.html A collection of easily stated conjectures which are still open. Each conjecture is stated along with a collection of references.
Mathematician's Secret Room - http://www.asahi-net.or.jp/~KC2H-MSM/mathland/overview.htm Unsolved problems in Number Theory. English and Japanese text by Hisanori Mishima.
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