I got the new Battletech for Christmas and I've been musing on how similar it is to X-Com and Jagged Alliance.
I also recall a game for the SNES that was never released in the USA but was given a translation patch by fans called Front Mission, although I never got my hands on any sequels.
I liked the turn-based tactical RPGS like the old Gold Box games and Spiderweb Software's old Exile series for the Mac (remade as the Avernum series), and the fan translation of Bahamut's Lagoon for SNES (I found a bunch of translated RPGs for the SNES back in the early 2000's when money was tight, might not have been strictly legal).
I heard a game called Warhammer 40K was supposed to be similar, but when I found Dawn of War last year at the library "Book Sale", it turned out to be a RTS that tests my reflexes and hand-eye coordination (as well as how good a condition my mouse is with only enough space for a traditional mouse mat for mousing around, making precision not as good as if I had more room), so that was a disappointment, unless that was the wrong game. Those book sales are pot luck, you never know what you're going to find. It's how I discovered X-COM.
So, what else is out there similar to Battletech or X-com? I don't really care how old it is, if it's for the Apple II I've still got my old Apple IIGS in my mom's basement and I can use DOSBox. I've also got a Windows 98SE/XP dual-boot computer available for games that don't like Windows NT (which 2000 and later is based on and descended from as opposed to Windows 95/98/ME).
Older might be better to a certain extent since it is usually available cheaper, but I don't care about age. I still think Dungeon Master is one of the finest computer games of all time, and I enjoy Baldur's Gate II.