Do you have Kidspiration and an interactive white board? If so, you have access to lots of great goodies for building engaging math lessons! Under Activities, you'll find ready made lessons, and you can build your own math lessons using the Math View. That's exactly what I did to create the lesson for adding and subtracting decimals shown below.
To help you get the most out of this lesson, I created a video tutorial using Screencast-O-Matic. Click here to view the tutorial and click here to grab your copy of the Kidspiration file. When you do this activity with the class, I recommend adding a concrete component by having the kiddos use base-10 blocks and place value mat at their desks to duplicate what you are doing on the interactive white board. You can grab a decimal place value mat here. Model the first problem and have all students work along with you using the base-10 blocks. After that, select different students to help you with each of the problems on the interactive white board while the rest of the class uses the base-10 blocks.