I have so many books that I have read multiple times and would definitely read again.
Harry Potter series
Hunger Games series
Scott Westerfield's Uglies series
Ellen Hopkins books
Willow
My Sister's Keeper by Jodi Picoult
David Pelzer books
Switching Time by Richard Baer
Go Ask Alice
Come Back by Mia and Claire Fontaine
There are so many more but these are what I can think of for now.. what are your go-tos when you have nothing else to read?