Fates Warning...the early stuff was completely revolutionary, practically invented the modern genre of prog, although it can be a bit hard to take for the uninitiated...the latter day stuff shows a maturing band that substitutes riffing and time changes for style and shading...no one sounds like Fates. I recommend Awaken The Guardian for the early stuff and both Parallels and A Pleasant Shade of Gray
Pain Of Salvation...wow...definitely no one sounds like them. POS delves into the human condition with emotion, intensity, and musical eccentricity. Again, for the uninitiated, a little hard to take at first, but damn it just seeps into your pores...
Other very competent "prog" bands of various degrees: Vanden Plas (stylish and refined prog), Threshold (heavy, but catchy British prog), and Spock's Beard (jazz influenced prog).
Any other thoughts on this from the peanut gallery...?