The paper $``$One Hundred and Two Problems in Mathematical Logic$"$ by Harvey Friedman is an article that lists 102 open problems in mathematical logic.
These problems were selected so that it is about as likely that the solution to the problem would be a positive solution and a negative solution. For example, the P vs NP problem would not be a good problem for this list because it seems much more likely that $P\neq NP$ than $P=NP$. The paper was written in 1975 so this list of problems is quite old.