The first one is "Un Lun Dun" by China Mieville. While the idea of a Young Adult novel by this famously profane author is a bit croggling, I found this a very good book. It is also an interesting example of how highly creative authors can take similar premises and do something very different with them. In this case, the premise, that there is a shadow London (UnLondon) co-existing with the one most people know, is familar to readers of Neil Gaiman's "Neverwhere," but Mieville's treatment is quite original.
UnLondon is actually in the next dimension over, and lies on a slightly lower entropic chord. It is where much of what is lost, discarded, or unwanted goes, including everything from broken umbrellas to redundant bus conductors. The adventure begins when two girls find a way through to UnLondon. They are soon caught up in a very familiar sounding type of story involving the "chosen one," a "Prophecy," an elaborate quest situation, and a brooding and pervasive enemy. However, Mieville quickly turns all the conventions topsy-turvy in a way that had me saying, "Oh, yes!"
It wouldn't be a Mieville work with out his trademark grit, dirt, and grunge, but he has managed to write a quite remarkable, very engaging and enjoyable story without the sex, gross violence, or adult language that mark his "grown-up" works. Recommended for young adults and other adults that still enjoy a good fantasy.