Loot!

Loot and the cool factor is what drives people to keep playing. If you want people to stay playing long after they've maxed lvl, add this stuff...

-socketable stuff
-gems to socket with
-SETS! a great way to keep people playing and grinding
-how about neck equips or rings??
-maybe a way to "refine" your gear for +1, +2, etc...
-put a LOT of work into creating cool armors and weapon meshes, this is what makes WOW awesome
-more glowing effects on gear

Remember: Loot is what makes this type of game great!

Well you could have some purely cosmetic but very rare things which when yuo find make your character look more awesome. Im fairly sure loot would lead to quite a bit of disapointment, at least till a trade system is introduced as it would be no use to me to find the ultimate rare sword of where ever as I am not a tank.