I think a good starting point would be this thread:
http://www.giantitp.com/forums/showthread.php?t=210675
I haven't played that many games on his list, but here's my take on the few I have played:
XCOM: UFO Defense is a bit dated, but still a fabulous game. It's the main progenitor for
western tactical RPGs, much like Fire Emblem is to Japanese ones. The "RPG" element is pretty light in it; it's more of an alternate strategic / turn based tactics game. XCOM: Enemy Unknown (the 2012 reboot) is a quality re-envisioning which keeps a lot of the same elements that made the original successful, while simplifying and streamlining a lot, and adding more modern graphics, UI, and audio. That said, it drifts even further from games like the Fire Emblem games.
Battle for Wesnoth is probably
the best free, open-source game I've ever played. If you like Fire Emblem, I think you'll probably like it; it's also a bit lighter on the "RPG" aspect. You can go download and try it yourself whenever you want:
www.wesnoth.org
You'll probably find the "battlefields" in Heroes of Might and Magic to be much smaller and more limited than those you are used to, and the "RPG" elements are relatively unimportant to the game as a whole (your heroes can, for the most part, be pretty well described as bags of stats and abilities with a name attached). That said, personally I loved Heroes 3. If you liked the combat in the HoMM games, the King's Bounty series (starting with the 2008 "sequel" of KB: The Legend) was made by a lot of the same developers (after switching studios) and really plays like a prolonged series of set-piece skirmishes in HoMM, with the "strategic" half of a HoMM game replaced by a lightweight RPG. It can be good fun, although I found that the game began to drag after a certain point (many of the fights can become tedious and repetitive).
Age of Wonders never really grabbed me. I played a few games in the series, but found it hard to remain interested. Maybe it'll be different for you.
I haven't played Avernum, but I did play Avadon (which is by the same developer, and is supposed to be very similar). Avadon is very light on the "tactics," but is a pretty good indie RPG reminiscent of lots of old-school 3D isometric RPGs. If you're looking for "the PC Fire Emblem," you'll probably want to look elsewhere.
