Faster movement speed. On the whole, a lot of time is spent travelling. Really increased movement speed would make PvP a trickier affair, so I'd suggest a momentum system. The longer you run - without being involved in combat - the faster you get. Up to a maximum limit, of course. So you'd run at normal speed for the first 5 seconds and it'd take 20 or so seconds to attain <a href="http://www.albionmall.com/">AO Silver</a>. This would mean movement abilities are still worth having for PvP, but for travel and PvE it would cut down travel time.
The world is small at the moment and I think I remember seeing that the final size is estimated to be 20x what we have now. If that's the case, then given the limited options for traversing the world, faster travel is really needed. The other option would be the old horse route system between major cities, but I think that's a little more limiting.