What's the proper way to write custom code when the order is processed?

I need to make a web service call to start a workflow once an item is purchased.  I can edit the OrderProcessingService.PlaceOrder method and put my code at the bottom, but I was wondering if there was a better way to do this, maybe using a plugin or something.  Any advice?

Create a plugin that handles Order Update Events


    public class MyPlugin : BasePlugin, IConsumer<EntityUpdated<Order>>

thanks a lot, that works for me.

Works well for me too.

I think the post I was replying to was removed.  Disregard this.