Try Runes of Magic actually combos exists there like PvP system is even best out of free ones.
runes of magic is slow paced crap combat like wow if you want fast paced combat try rohan or sun online but rohan is bs infested youve been warned sun is good though shin magumi tensais imagine has a combo system but its stiff and frustrating at times other than that im not really sure to many games out there trying to copy WoW so its hard for guys like us to get that adrenaline combat we crave
well, there will be one good combo game in future, Divine souls, just went cb test past month. realy liked, atleast gameplay, dmc like combos +rpg like skils, interesting mix, game itslef is kinda mo-mmo, GW style, hawe few common maps, other is instanced. think each class hawe around 20 combos, not sure if there will be more
p.s. just because u can use couple skils in some special way to increase theyr power, ist actualy action game like combos .... coz then most of games hawe "combos" ... ( if u count that in rom,rohan, sun, or ewen wow, there is ...)