Links and resources
Various math competitions for university students in the world:
SMMC - Simon Marais Mathematics Competition (analogue of Putnam in Asia-Pacific)
IMC - International Mathematics Competition for University Students
VJIMC - Vojtěch Jarník International Mathematical Competition
Putnam - William Lowell Putnam Competition
SEEMOUS - South Eastern European Mathematical Olympiad
KCMC - Kansas Collegiate Mathematics Competition
VTRMC - Virginia Tech Regional Mathematics Contest
ISMO - International Scientific Mathematics and Chemistry Olympiads for University Students in Iran
MH9000 - Mathematical Problem Solving.
Regular course at NTU with a lot of interesting problems. A lot of them are taken from the known competitions though, so don't expect much from this link:
Below you can find all problems from NTU math competitions (with solutions) and from NTU selection tests (without solutions).