I remember reading both 'My Brother Sam is Dead' and 'Johnny Tremain' in fifth grade; I actually enjoyed 'My Brother Sam...' much more. That same year, we read 'Across Five Aprils' by Irene Hunt (set during in the Civil War) and 'The Witch of Blackbird Pond' (set in the 1680's colonial period). I remember them being quick but engaging reads. Between these and Scott O'Dell ('Island of the Blue Dolphins', etc.), I developed a life-long love of historical fiction.
When I was your age, I read 'The True Confessions of Charlotte Doyle' by Avi, and loved it. The book is set at sea during the 1830's; not only is it incredibly detailed and well-researched, but I found the story fascinating.
I also second the above recommendation for Harper Lee's 'To Kill a Mockingbird'; wonderful, classic novel.
If you enjoy fantasy, I suggest the following:
* CS Lewis' 'Chronicle's of Narnia' and JRR Tolkien's 'The Hobbit' and 'Lord of the Rings'. Must-reads for any fantasy fan.
* Lloyd Alexander's 'Chronicles of Prydain'. Fantasy inspired by Welsh mythology.
* Raymond E Feist's 'Magician: Apprentice' and sequels. High fantasy (magic, dragons, that sort of thing), but not as dense as, say, Tolkien or George RR Martin. The first 2 especially are a fun read.
* Neil Gaiman's 'Stardust' and 'Coraline'. Gaiman is a brilliant, creative author, and these two books are good for teenagers. 'Coraline' is delightfully creepy; 'Stardust' is a more whimsical tale, about a young man's quest through Faerie realms.
* Terry Pratchett, both the 'Discworld' series (funny, funny stuff!) and the 'Bromeliad' trilogy ('Truckers', 'Diggers', and 'Wings'--I *adored* this series).
* Terry Brooks' 'Magic Kingdom' series. I never got into his Shannara books, but these were favourites of mine for years.