To improve the active combat and to give players different animations from the start the number of attacks and the attack speed should be the same from BAB 1 to 20. A player should perform the four different attack animations in the same order with an attack speed of perhaps 1 attack / 2 seconds (ranged), 1 attack / 1.5 seconds (one handed and two handed) or 1 attack / 1 second (two weapon fighting and unarmed).
The damage of main hand and off-hand attacks is increased at BAB 5, 10, 15 and 20 by the base damage of the weapon. For example a dagger would have a damage of 4D4 at BAB 18 (1D4 base + 1D4 at BAB 5 + 1D4 at BAB 10 + 1D4 at BAB 15).
Two weapon fighting feats should reduce the attack penalty (Without Two Weapon Fighting: -10, Two Weapon Fighting: -4, Improved Two Weapon Fighting: -2 and Greater Two Weapon Fighting: +0). Power attack should have a -2 attack penalty and should increase the damage by BAB x 0.5 (one handed weapons) or BAB x 0.75 (two handed weapons). Rapid shot should increase the attack speed of ranged weapons to 1 attack / 1.5 seconds.
These changes could improve the active combat of DDO, could reduce the need of inflated monster AC / HP and could make grazing hits useful at high levels.