USA Mathematical Talent Search

http://www.usamts.org/Problems/U_Problems.php

http://www.usamts.org/Problems/U_ProblemsPast.php  (FULL LIST)

For eg (a sub-list):

Year 23 (2011-12)

Round	Problems	Solutions
Round 1	Round 1 Problems	Round 1 Solutions
Round 2	Round 2 Problems	Round 2 Solutions
Round 3	Round 3 Problems	Round 3 Solutions

Year 22 (2010-11)

Round	Problems	Solutions
Round 1	Round 1 Problems	Round 1 Solutions
Round 2	Round 2 Problems	Round 2 Solutions

Year 21 (2009-10)

Round	Problems	Solutions
Round 1	Round 1 Problems	Round 1 Solutions
Round 2	Round 2 Problems	Round 2 Solutions
Round 3	Round 3 Problems	Round 3 Solutions
Round 4	Round 4 Problems	Round 4 Solutions

Year 20 (2008-09)

Round	Problems	Solutions
Round 1	Round 1 Problems	Round 1 Solutions
Round 2	Round 2 Problems	Round 2 Solutions
Round 3	Round 3 Problems	Round 3 Solutions
Round 4	Round 4 Problems	Round 4 Solutions