Yeah, so I'm not doing one a day, but I guess you've all figured that out already, eh? ;) I'll just post a new "day" whenever I have the time and it fits my usual schedule.
This question was actually a lot harder than I first thought. I went back through my list of read books trying to remember how they made me feel while I was reading them, and I realised I don't read all that many feel-good books. However, reading Harry Potter and the Philosopher's Stone made me happy because it's such a great start to a wonderful series, and besides enjoying the fun and excitement while reading, you know that this is only the beginning.
Stardust by Neil Gaiman also made me happy, and even though I haven't read it yet, The Girl Who Chased the Moon by Sarah Addison Allen make me happy just by looking at the beautiful whimsical cover and feeling the anticipation of delving into it.
Just give me a bit of magic and I'll be happy. :)
Which book makes you happy?