Toribash
Like they said,use a filter like alien glow or neon on whatever you want to glow.

If you look around the net you'll find even more scripts & filters that'll do a better job.

<Erf> SkulFuk: gf just made a toilet sniffing joke at me
<Erf> i think
<Erf> i think i hate you
GIMP support =/= Toribash support. Use Google.
"Call yourself alive? I promise you you'll be deafened by dust falling on the furniture,
you'll feel your eyebrows turning to two gashes, and your shoulder blades will ache for want of wings."