In System Siege, we have a number of explosion animations that are drawn frame-by-frame. This process can be time consuming, but the overall effect is quite nice.
Here we have a simple explosion animation:
Although fairly uninteresting on its own, there are several simple ways to spice it up without too much additional work. For example, simply changing the colour can provide a new twist/angle on the animation.
Additionally, we can achieve another effect by multiplying the initial explosion animation and offsetting its start time.
Finally this principle can be taken to an even more extreme by adding more explosions.
In short, one simple animation can go a long way!