I agree with all of the posts here. My favorites of those listed are:
Heroes of Might and Magic 3 - This is TBS perfection
Heroes of Might and Magic 5 - The gameplay is a little easy compared to 3 and also a little meh. However, I loved the Tribes of the East expansion. The way they did the Barbarians is one of the best implementations of a "Might" race that I have seen. Really, TotE really makes HoMM5 "fun" for me.
King's Bounty & Armored Princess expansion- This is basically HoMM with a focus on Hero development and no castle management. It's a little easier than HoMM because you don't have to worry about that stupid scout hero that's flagging all of your mines behind your lines and it's a little more pure tactics rather than grand strategy. It has a much stronger focus on story (and it's actually pretty good), but overall it's a lot easier.
Master of Magic - This is an awesome game, but I can't play it now anymore. I've been spoiled and just simply can't go back to 320x200 graphics. Perhaps you can. The complex gameplay though, from the sheer amount of magic, races and troops is still something that hasn't been replicated.
Disciples II - This game is interesting. It simplifies the tactical combat quite a bit; there's really no movement involved, no magic (all magic is on the strategy map) and units just sort of bash away until you win. It's more of a pure strategy game with a tactics minigame. Not really my cup of tea (just for it's playstyle) but it may be for you.
Other games that I haven't seen listed here:
Fire Emblem series - This is one of the definitive TBS's on the Game Boy/DS hardware. It almost completely tactics focused; your strategy is really related to how you gear your units, but it's a lot of fun. All the units are "heroes" in the sense that they have a storyline, they talk to each other in battle (you can gain support for each other if they fight together often which can lead to romantic outcomes). In addition, the game features permanent death, so your heroes can actually die (and it's reflected in the storyline). It's a great game, but sometimes, mind-numbingly hard, especially due to 2 points. 1) All stat generation is RNG. This is cool because in one game you might have Edgar the super buff knight, but you might also have Edgar, the worthless you guy stash on your bench because his stat growth was terrible. 2) If you're trying to beat the game without losing anyone to permanent death...prepare for a LOT of reloads. The storyline is very strong due to all the interaction of all the units and the beautifully hand drawn anime-style cutscenes.
Other games that you might enjoy but don't fall under the aegis of TB Fantasy RPG/RTS:
War of Eustrath - This is a Sci-Fi TBS on the iOS platform. It's a lot of fun; you run around in killer robots to kill other killer robots. It's storyline is pretty good too; it has anime-style cutscenes to tell the story and your robots have attacks governed by "Will", which is sort of like Mana Points except the more Will you have, the stronger your attack and defense too, so you have to decide if the spell you're using is worth the Will since it will affect your normal attacks as well and "Energy/Ammo". Your best attacks in the game use both Energy and Will so it's a careful balancing act.
Civilization 4 - This is a TBS, but it's not really fantasy. Civilization is pure strategy; not really a ton of tactics, but it's done in a very polished and fun manner. I'm not going to go too much into this because most everyone should know what this game is.
Front Mission 4 - This is a Sci-Fi TBS on the PS2. Again you control giant robots to kill other giant robots. The storyline is sort of cheesy and disconnected, but the cool part is buying parts and upgrading your robot. You want a shotgun? A sniper rifle? Heavier armor? Self-repair? You can have all of these, but you have to balance the weight and power requirements of the gear. In addition, the pilot level up system is amazingly complex. The focus is mostly "upgrading your pilot/robot to crush all beneath your giant foot".
X-Com series - This is another Sci-Fi TBS on the PC. It's the "Heroes of Might and Magic" for Sci-Fi TBS; IE. it's perfection. You have to kill aliens (hire soldiers!) and capture their technology so you can research them for your own use (hire scientists!). Then you can reverse engineer their technology to make your technology better (hire technicians!). Meanwhile, you have to protect countries on Earth by shooting down UFOs and stopping their terror attacks (tactical gameplay is amazing). This is the perfect meld of strategy and tactics.
