According to the Star Wars extended canon, there are 7 different lightsaber fighting techniques. A few of these are used by characters in the movies, such as style 2 by Count Dooku, or style 6 by General Grievous. However, none of the styles fluidly integrate an aggressive use of The Force and lightsaber dueling. What mechanics of the Force, or technicalities, prevent a true pinnacle fighting style, without an obvious lean towards defense or offense. (I am not counting style one, since it is the base technique for all other styles.)
The Force is VERY heavily used in lightsaber combat, just not in the obvious fling-stuff-around way. After all,
A Jedi uses the Force for knowledge and defense. Never for attack.
I think the best description of how the Force is used in lightsaber combat that I've seen comes from the novelisation of Revenge of the Sith:
Three MagnaGuards...were certainly beyond Obi-Wan's ability to defeat, but it was not Obi-Wan who would defeat them; Obi-Wan wasn't even fighting. He was only a vessel, emptied of self. The Force, shaped by his skill and guided by his clarity of mind, fought through him.
In the Force, he felt their destruction: it was somewhere above and behind him, and only seconds away.
He went to meet it with a backflipping leap that the Force used to lift him neatly to an empty droid socket in the ceiling hive. The MagnaGuards sprang after him but he was already gone by the time they arrived, leaping higher into the maze of girders and cables and room-sized cargo containers that was the control centers superstructure.
Here, said the Force within him, and Obi-Wan stopped...frowning back at the oncoming killer droids...Though he could feel its close approach, he had no idea from where their destruction might come...until the Force showed him a support beam within reach of his blade and whispered, Now.
His blade flicked out and the durasteel beam parted...and a great hulk of ship-sized cargo container that the beam had been supporting tore free of its other supports...and crashed down upon all three MagnaGuards with the finality of a meteor strike.
Oh, thought Obi-Wan with detached approval. That worked out rather well.
That was the true power of the Force in combat - not to throw things at people, but to know and perceive things faster and more completely than a brain - or even a computer - possibly could.