I really like Symphony X, but haven't really stumbled on other progressive metal bands that I would return to listen to (although to be fair I haven't looked very deep into smaller bands).
I'm interested in hearing bands that you think are either similar to or general recommendations from someone with similar tastes.
To me SX just finds a cool balance of being at the same time over the top but still a bit restrained and melodic (with "good taste")
Symphony X is one of my favorite bands, you might also like Pagan's Mind. Awesome guitar riffs, great songs, vocals take some getting used to but he's a great singer. Also one of my favorite bands. Check out the album Enigmatic:Calling.