Khan Academy
Khan Academy: Add and Subtract on the Number Line Word Problems
Practice adding and subtracting using the number line. Numbers used are 100 or less. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video or receive hints.
SMART Technologies
Smart: 65 Addition/subtraction Story Problems
Students may compare, join, separate numbers to solve these story problems. These are the tougher kinds of problems! There are also some of the more traditional, "easier" part/part/whole type of story problems here, as well.
Other
Math Stories: Write a Number Sentence
At this one page site you can work through step by step a sample problem that illustrates the problem solving strategy for "Write a number sentence." The answer is right there to help you check your thinking.