Progarchives is a great place to learn about different prog bands. They do have a progressive metal section however they are all groupewd together. ie you wouldn't find Dream Theater and Opeth seperated even though one is Progressive metal and the other progressive death metal. Also like someone else said, there are less extreme bands on there.
I am a huge fan of progressive rock and progressive metal. One of my favourite progressive metal bands right now is Threshold. They are complex but at the same time very catchy. I am also a big Dream Theater fan and reccomend them for anyone starting out in progressive metal. An album like Images and Words would be considered the ultimate progressive metal album. Check out Dream Theater and Threshold for progressive metal. Also check out Shadow Gallery, Star One, and Liquid Tension Experiment (prog metal with dream theater members, no vocals).
Progressive rock wise Some of my favourite bands include Spock;s BEard, Porcupine Tree, Rush etc... I really reccomend those bands.
Also if you want a really technical band check out Spiral Artichet. I am not a fan of this band however as they seem to be over technical. Most prog i listen to is very technical but still sounds great. Spiral Artichet on the other hand seem so technical it doesn't sound that good.