Quests: it's nice to be able to get some free experience without sitting through the really low levels in some skills. Albeit, it would be nice to get the first 30-40 melee levels through quests.
Clue Scrolls: they make the game more exciting. I also love pickpocketing H.A.M members for level 1 clue scrolls.
Skillcapes: they are a really good motivator. They keep people playing longer. Is there any information on if these are being considered?