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!