Well if you are looking for something similar to DT, then Circus Maximus is the first thing that comes to mind. Their style is pretty similar to late 80's/early 90's DT. Also, if you have not yet checked out Queensryche or Fates Warning,the I highly suggest you do so, as both bands are really Dream Theater's forerunners in the prog-metal movement, and both were a huge influence on DT. If you check out Queensryche, I highly recommend any album from '84 to '91 as much of their best work is from that time period. As for fates warning, if you want to get into their more progressive side, then their material from 88 to 2000 should suffice, in particular I would recommend the "A Pleasant Shade of Grey" album from 97, one of the most complex and beguiling concept albums in existence. Other then that..... there was a UK band called Balance of Power in the late 90's/ early 2000's that had many similarities to DT, in particular their 2nd, 3rd and 4th albums ("Book of Secrets" "Ten More Tales...." and "Perfect Balance", respectively); just avoid their last album ("Heathen Machine") as it is very generic euro power-prog. Enchant is another great prog-metal band, as is Pain of Salvation. And if you want something more obscure, back in the early '90s there was a little prog band called Kingsbane who sounded like suspiciously similar to Majesty/Dominici era DT and released a six song demo in 1991. They later went through a number of name changes and eventually released a full album called "In The Name", but that original 1991 demo is still their best work. I will post later if any other bands come to mind, but that should be enough to get you started.