See my avatar? Why not add one of those guys in? It'll sure spice things up in your aquarium!
Seriously though...I'll assume that you want to keep those little guppies alive. Adding more/fancy ones is not a bad idea.
I know you said you weren't as interested in the neon tetras---have you considered bloodfin tetras though?
These are great little schooling fish have whitish/silverish bodies with bright-red colored fins.
They will not get beyond 2 inches in length (more like 1.5, actually...esp. in a smaller tank), and they live for a very long time. They are quite hardy, peaceful, yet seem to have individual personalities that might really spice up your tank.
I would think that 4 of these would do just fine with your 3 guppies. Your 5 gallon tank should handle this no problem; just so long as you keep up with water changes, etc.
Sorry I don't have a pic or link to give you at the moment---Just perform a search for "bloodfin tetra" if you wanna see what they look like.
Hope this helps.
Big Vine