I believe I posted this suggestion a couple years ago, but now that a lot more custom content is being added, it might have a better reception. Many other games have implemented achievements with great success, I believe WoW was one of the first ones. Now pretty much every console game has achievements or trophies for completing in-game content.
I would propose rolling out a number of basic achievements, and adding new ones every couple months so there's always something to do. Rewards could be non-tradeable cosmetic items, resources, consumables, etc.
Example achievements:
Kill 500 bears - Reward: Bear-skin cape
Fletch 50k mith arrows - Reward: Blue magic longbow. Like a regular magic longbow, but... ya know... blue.
Recharge your prayer points at every altar in-game. Reward: 50 dragon bones
Consume 800 redberry pies - Reward: Pie face (wearable head item that just adds pie smear to the face of the char)
Complete 300 medium clue-scrolls: - Reward: 1,000 law runes
In addition to actual in-game items, you could develop a title system similar to other games. This would appear above the players head in front of or after their name (if player names are turned on in interface options). It would not show up in chat or on global. Then you could have a number of achievements that grant a unique title, such as "Dragon Slayer" Paul for slaying 2,000 dragons.
Like the upcoming slayer skill, this will make players complete content, kill different npcs, and work on skills in ways that they wouldn't normally do. It would also add a new highscore option - Achievement Points. Points would be awarded after completing an achievement, the amount would vary based on the difficulty of the achievement.
Vet Paul
Iron Paul
Paul
[img]http://i.imgur.com/or9jdo2.png[/img]