Usually, a good battle system is not what drives me through an RPG. In fact, it's usually the other way around- everything else the game has to offer helps me tolerate it! There are exceptions of course, and here are a few of mine.

Valkyrie Profile 2: Silmeria
I have not played the first VP, but this game is a prequel, so that wasn't necessary. This game may have my favorite battle system ever. You take control of four characters all at the same time, and move around the field and attack in real-time. You can split up and move characters individually as well, but at a cost. In order to attack enemies efficiently, you must have your party work and attack together. Doing so enables you to build up combos and break off pieces of the enemy which will become items and equipment. It's very difficult to get the hang of, but immensely satisfying once you do.

The Golden Sun series
Actually, this series' battle system is an extremely basic turn-based one. But battles are quick, meaning the randomly occuring battles aren't as much of a hindrance or annoying as other RPG's can be. The element-based pwers and Djinn system is what makes the battle system more interesting than other turn-based systems.

Final Fantasy XII and Xenoblade Chronicles
I'm putting these two together because they are very similar in some ways. I like being able to initiate battles on-the-go and being able to continue immediately after it's over. The battle systems are also deep enough to remain enjoyable throughout these 100+ hour games. In FFXII, the system becomes especially reliant on the gambit system about halfway through the game, which allows you to essentially create a list of "if>then" strategies, allowing you to directly tinker with your party's AI. In Xenoblade, on the other hand, you learn different special attacks over time that can change the flow and strategy of battle, keeping the game interesting for the long journey ahead.

Any that you guys would like to share?

I like Mount & Blade Warband which has a real time combat system.
- You can use different slashes, thrusts and overhead strikes to attack the enemy.
- Incoming attacks can be parried with your weapon or blocked with a shield.
- You can ride a horse and attack with a couched lance (extremely deadly).
- No potions or magic exist.
- With a good computer, you can have up to 1000 men on the battlefield that follow basic orders
- This game has armour values and three different damage types (slash < pierce < blunt)
- M&B Warband has lots of melee and ranged weapons: swords, spears, crossbows, bows, axes, pikes, lances, hammers, maces etc.

I like a hack and slash combat system as used by companies like Falcom with their Ys games. Why do I like it? Well for one thing it's easier to dodge attacks as you can move around while attacking and you can string together continuous attacks by pressing the attack button repeatedly and if you get hurt, you can quickly open up a menu to use a health restoration item (you can in Ys Seven) or just pick up a dropped health restoration item from a monster (as used in Ys The Oath in Felghana and Ys Origin)

Gambit from FF XII. Once you get around with, lots of possibilities open.

I really enjoyed the turn based system in FFX where you could switch out characters mid battle to use as you saw fit.