*sigh* I always feel like the bad guy..
But.. my friend.. your tank is HORRIBLEY overstocked! You cant keep an angel in a 5 gallon! It will QUICKLY out grow that tank, reaching sometime,s up to 18 inches from tip to tip. Half your angel would be out of the water! You need atleast a 20 or 29 gallon tank for the angel alone.
The neons? The angel will EAT the neons. Right now the nagel may be small, but not for long. And you have WAY too many in there. Does your tank not look like a pet shop tank? Do you not NOTICE your craming your fish into unaccepttable, horrible conditions?
Your guppy died most likely from filthy water and not nearly enough room to move. I wouldnt be surprised if your angel did some damange either.
Please, fix this, because that has got to be the worst over stocking case Ive come across in a while.
Dakota