What is the most beautiful supernova you've ever seen?

Supernova 1987A.  One of the closest to Earth - so we have incredible pictures.

You should look up the 'Messier Objects.'  There are 110 of them and they contain planetary nebula (the things you're talking about), diffuse nebula, star clusters and galaxies.  They're the common things for amateurs to look at because they're bright and usually pretty.  Or you can just search for images of 'M1' through 'M110'.  Off the top of my head I know you'd be interested in M1, M27, and M57.  Or just search for planetary nebula.

Search for the Sombrero galaxy too.  It's a galaxy so it's not what you're asking about, but it's just so cool

A supernova itself doesn't make for a great picture: it's just a blindingly bright star. What's neat is the debris that it leaves afterwards.  A good example is Messier 1, the Crab Nebula, a supernova that exploded in 1054 AD. The Veil Nebula is a remnant of a much older supernova. Even more exciting is the Eta Carinae Nebula: a supernova just waiting to happen. I had a wonderful view of this through an 18" Dobsonian telescope in Australia last month.