Adnan Masood's Weblog! عدنان مسعود

Keith Delvin in "The Millennium Problems: The Seven Greatest Unsolved Mathematical Puzzles of Our Time" ASIN 0465017290 which was recently reviewed by Guardian describes the following as seven greatest mathematical puzzles.

1. Riemann Hypothesis
   http://match.stanford.edu/rh/
   
2. Yang-Mills theory of Mass Gap Hypothesis
   http://ccollege.hccs.cc.tx.us:16080/instru/Math/faculty/sever/2413%20Summer2003/21thCenturyMathProblems.doc
   
3. P VS NP Problems
   http://www.claymath.org/millennium/P_vs_NP/
   
4. Navier-Stokes equations
   http://en.wikipedia.org/wiki/Navier-Stokes_equations
    
5. The Poincare Conjecture
   http://www.math.unl.edu/~mbritten/ldt/poincare.html
    
6. Birch-Swinnerton-Dyer Conjecture
   http://mathworld.wolfram.com/Birch-Swinnerton-DyerConjecture.html
    
7. Hodge Conjecture
   http://mathworld.wolfram.com/HodgeConjecture.html

I googled and saved links for later reading; Not in a position to say of they are seven greatest of all times but they pretty much look like it.