My Combo Tracker will display a scrolling text on your screen ranging from 0 Combo Points to 6 Combo Points. Once you reach 5 Combo Points you will get an audible alert, that's for Sin. Once you reach 6 combo points for Sub and Outlaw you will get and audible alert. Right now there are 10 different alerts to choose from. You can also choose from different fonts, as well as a color picker to change the font color. You can also adjust the the size of the fonts in the Options/Addons interface. See the include image to see the menu.
Be aware that this is for Rogues only. I do plan to add other specs....