World of Warcraft Spotlight
This addon will provide you with detailed information on the requirements for your character's next level.
In addition to the amount of experience needed, it will tell you how many kills are left and how many quests you need to finish. Besides quests and kills, the addon also takes into account the remaining dungeons, battlegrounds and crafted items. On top of that, it even calculates how long all of that will take. These details are displayed in a bar, allowing you to keep track of the current requirements at a single glance.
Additionally, the addon can be configured easily by using either the /xtl command or the /xtolevel one.
Simply clicking the "Install via Curse Client" button found on the main page is all you have to do to install this addon.
XToLevel is an excellent choice if you would like to know more than just the required amount of experience for reaching your next level.