Producing graphic images on a PC can sometimes feel like a hurdle. Sure Microsoft have introduced SmartArt whose predefined formats can be a blessing when they correspond to what you need but are a barrier the rest of the time.
Can I introduce you to Grafio, my favourite app for diagramming on the iPad - not forgetting of course that anything you draw on your iPad can be used on your computer in documents you are working on there. Grafio makes creating amazing looking diagrams both easy and fun - I love it! It's not just me either, I know one deputy head who loves Grafio so much that she uses it capture ideas during meetings and shares the resulting work as people leave the room.