I would put the Jethimadh Tower on the top of this list. If you haven't got time to explore the Tower or do the quest with the keys, at the very least go to the Tower museum and listen to the story of Ur.
what else? hmm. Some of the quests are a bloody pain (like that perter out peat quest where you have to co ordinate your peat digging with several other people using internet connections of varying speeds - ugh) I like kristol Kaos seam street. There are also lots of new streets I haven't seen yet (some underwater group of streets somewhere...with fishing. something about a dinoseaur. and I just yesterday discovered where to scrape Ice).
I enjoyed the Llimski jones rescue thing (can he please please come to the End of The World party without evaporating? please?)
Other "must see" suggestions for lower level players?