Cool Math
Coolmath: Coolmath4kids: Adding Numbers Within 100
A step-by-step tutorial showing how to add 2-digit numbers in place value columns without regrouping. Includes exercises to try. CCSS.Math.Content.3.NBT.A.2 Fluently add and subtract within 1000
Khan Academy
Khan Academy: Add 2 and 3 Digit Numbers (No Regrouping)
Practice solving problems like 243 + 452. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video or receive hints.