ClassFlow
Class Flow: This Doesn't Add Up!
[Free Registration/Login Required] This flipchart teaches the steps in adding 2 or more digits with regrouping and gives students practice problems.
Khan Academy
Khan Academy: Add 2 Digit Numbers (No Regrouping)
Practice solving problems like 24 + 45. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video or receive hints.