its funny, i dont destinguish between whether a book is 'serious' or not - i just bloody read what takes my fancy. Some days it might be harry potter or terry pratchett, some days it might be Micheal Moore or Mark Thomas. some day it might be Micheal Cunningham or Huruki Murakami Some days it might be Nietzsche or Ronald Dhahl.
Curently most of the books i seem to be reading are either about food (Anthony Bourdain or Jeffrey Stiengarten) or , quite obviously, guitars (too many to list).
i am also enjoying graphic novels like 'v for vendetta' and 'the watchmen'
Terry Pratchett books are simply phenomenal - Although I wouldn't say most children, or atleast younger children would have as easy a time reading them.
Wez - Naming Alan Moore stories is unfair - Nobody can compete with that :p
There are some superb Children's Books which are infinitely better than Harry Potter - The Abhorsen trilogy by Garth Nix comes to mind - As does The Tales of the Otori Trilogy written by Lian Hearn.
Also - For those who are into the whole Sci-fi thing - ANYTHING written by Dan Abnett is phenomenal - I'm not really into the whole Warhammer thing, but the lore and world they've made is phenomenal - And Dan Abnett is probably one of the greatest Authors I have _EVER_ read.
For more adult books - I'd say that The Count of Monte Cristo by Alexandre Dumas is one of the greatest books I have ever read - And The Three Muskateers also written by Dumas, while not as good as Monte Cristo was a great read too.
War And Peace is also phenomenal ofcourse.