Try the book: Fountas and Pinnell Leveled Book List k-8
It's a great resource for almost any book out there used in the elementary classroom. You might try some of their other books on Guided Reading. It's a great resource for understanding the whole reading process, especially ... Guiding Readers and Writers
You will find Third Graders to be challenging and lots of fun...a very delightful age. Not babies, but not yet grown up and "full of themselves". They're full of curiosity and love learning and most will really appreciate the attention and help you can give them on their way. Good Luck with your new position.