Number Munchers (classic)
Number Munchers (Wall of Game)
iXL.com (5th grade [challenge])
Other Math Games:
Convert Time
Convert time examples/calculator
Various units: Softschools.com
Capacity/Volume:
Length:
Area and Perimeter
Area
Multiply Fractions and Whole Numbers #1 or #2
http://www.teachingfractions.co.uk/
Comparing Fractions:
Balloon Pop:
Math Playground (comparing fractions)