BrainPop Educators has put together a nice lesson plan for teaching students about photosynthesis. I like game-based learning. Ruby Realm is a game that students can play to learn about photosynthesis. I like that it also helps students think about the processes and the chemistry that underlies photosynthesis and respiration.
Disclaimer: This game does require Flash. It also has vampires as part of the storyline.
Tip: To begin level one, click on the robot on the map. Also, to build the molecules, you may need to pre-teach the shapes of the molecules, or have students go to the help button to get a clue.