Take the High Ground has a photo tutorial on making some impressive looking smoke markers.
Here’s a tutorial on making explosion markers.
Here’s a bit of free software that helps you create magic style cards. I use the software to create unit cards for my miniatures games. They’re much better, both practically, and visually, than having unit sheets lying all over the table.
Big Lee has some instructions on making smoke and flames markers for Flames of War
Shadowkings has a set of downloadable bombardment markers for Flames of War.