Sherwinwilliams.com allows a student to pick different rooms (bedroom, bathrooms, etc.) and drag color onto the walls, trim, ceiling, and accent items.

icovia.com is a great room planner.  you can pick the size of the room and there are a ton of items to pick from to put in your room (it has everything from couches to kitchen items and even doors and windows to insert.  The only negative thing is students do have to sign up to use it if they want to save their project otherwise I have my students create it at home or during a class period. 
Amanda Conway, Riceville FCS Instructor

I also use the Better Homes and Gardens website or www.bhg.com
I have them find a dream home, use the color-a-home tab for the outside, and the arrange-a-room tab for furniture.
There is also one I found called See My Design Preview at www.seemydesign.com. It has one room that you can change lots of things in and then have the kids explain the elements and principles they used.
Rachel Reiter, Sumner-Fredericksburg FCS Instructor