Here I've got the same radial blur as before, but moved into a reusable class and drawn on top of the regular sprite. Surprisingly cool looking, I think I'll probably use it to indicate invincibility or some other powerup state. Especially if I animate the blur so it fades in and out.
The one snag is that because you can't have alpha in the textures you're limited to either no blending or additive blending. This isnt' too bad really as full screen effects (like heat haze) generally don't need blending, and glows are usually done with additive anyway.
I found this page of filters, and I think I'll be trying a few different ones out to see how they look. I've also got some old code for doing different types of blur for glow (mainly gauissian based) that I want to convert to this new way of doing things and test instead of the radial glow in the last post.