1) Storm by Brigid Kemmerer - This is one of my favorite paranormal romance series right now. The books are really fun, easy to read, and I love to sit down to read them in one sitting. A rainy day would be the perfect atmosphere to submerge yourself in this element-powers based series.
2) The Accident Season by Moira Fowley-Doyle - I got completely lost in this book and spent several hours listening to the end of the audiobook because I needed to know what happened. So reading this during a rainy day sounds like a good idea.
3) Wait for You by J. Lynn - This is a great contemporary. It is Armentrout's addicting writing mixed with a compelling story. I couldn't put it down and it gave me all the emotions.
4) The Ocean at the End of the Lane by Neil Gaiman - You could read this in one sitting. I would love to reread this on a rainy day! Such a great magical realism story!
5) Zita the Spacegirl by Ben Hatke - Go read this graphic novel! It is super cute and easy to read. It is all fun and games.