If you want to add a nice bloom-effect to your game, this library will help you.
It's a portable library, so it will work with all MG flavors and it is pretty simple to use. Just create a BloomEffectRenderer in your game, hook it up (Initialize and UnloadContent) and tell it to render the effect at the appropriate point in your draw-method.
Pass it a RenderTarget (source) where you've drawn all your stuff in, and a second one (target) where the output will be rendered to.
If you pass 'null' as the target RenderTarget then it will draw directly to the backbuffer.