Children's Book Recommendations

My daughter LOVED the Rainbow Fairies at that age. They are short chapter books about two best friends who meet fairies and help them. They are cute. They have the same premise in pretty much every book, which is good for that age, and definitely deal with friendship. Frog and Toad are also good friendship books.

As others mentioned, Magic Tree House are good first chapter books too.

Any of the Frog and Toad books by Arnold Lobel. Friendship is a huge theme, esp. Frog and Toad are Friends.

The Corduroy books by Don Freeman
The George and Martha books by James Marshall
Friends by Helme Heine
Best Friends for Francis by Russell Hoban
Horace and Morris but Mostly Delores by James Howe (I LOVED this one as a nanny)
Chester's Way by Kevin Henkes
Should I Share My Ice Cream (Elephant and Piggie books, Mo Willems)
Do Unto Otters: A book about Manners by Laurie Keller
Leo Lionni books, esp. Little Blue and Little Yellow

Anything by Petra Mathers. Anything. Also the same for Elisa Kleven, who creates wonderful characters. Some of the friendship books I love of hers:The Puddle Pail, The Friendship Wish, The Wishing Ball (all my preschoolers loved this one, and I did too) Ernst, and the Paper Princess Stories.

The Magic Treehouse series is great for K. They are short chapter books.
Anything by Bevery Cleary
The Laura Ingalls Wilder books

If she's starting to read on her own, you could get her the Frog and Toad books. Both my kids were given these books in K by their teachers. They are good books about friendship. And my little one loves dogs and so he LOVED the Biscuit books. They have very short chapters that a preK/K reader can easily read on his/her own.

ETA: Forewarning on the Fudge/Tales of a 4th Grade Nothing series by Judy Bloom. My older read these in 1st grade. He loved them. However, in one of the books (Superfudge), Peter (the 4th grader in the series) explains to his younger brother Fudge that Santa is not real and that parents bring the presents. So, if you choose to read these, be prepared for that. The third book in the series debunks the tooth fairy (this is probably a minor consideration if you've already debunked Santa in the 2nd book).

We didn't really read many chapter books at 5. One of my sons was super into Harry Potter, but not at that age. However, by second grade he took over reading them on his own. He is an avid reader though.

Here these were popular - but I think a tad bit later:

Rainbow Magic
Thea Stilton
Judy Moody

I liked Charlotte's Web but my kids didn't - until they read it in class in second grade.

ETA: Nervy's list is great. I second the Frog and Toad books. Forgot about those - that's more what we read (and Little Bear) for chapters books at 5. Excellent. I had them read to me during my childhood too - family favorites!

We also love Mo Willems. Knuffle Bunny and Piggy and Gerald are great ones.

These books were more what we were reading at kindergarten level.

My daughter is entering first grade. Some of the books I have read to her in the last year:
Ramona Series (Beverly Cleary)
Tales of a Fourth Grade Nothing / Fudge series (Judy Blume)
Ivy + Bean
Little House on the Prairie (I'd start with that one and skip Little House in the Big Woods, which is actually the first book in the series)
Charlotte's Web (that's a good one about friendship, too)

Don't read Harry Potter at this age. Save it for a few years when more of her friends start reading it.

My kids love Jan Thomas books. They are simple picture books, but very funny. We just saw a new one this week and my kids still thought it was funny (they will be in 3rd and 5th grade). Anything by Mo Willems is also great.

We love the Mercy Watson series by Kate DiCamillo. They are short chapter books. Easy to read in just a couple of sittings. Junie B. Jones, the early Magic Treehouse books, Boxcar Children, Betsy and Tacy series, Ivy and Bean series, Chicken Squad series, and The Trouble with Chickens are all good early chapter books to read to your daughter.

It really depends on her attention span. My daughter loved Charlotte's Web and the Little House books when she was that age. She would sit and listen to me read for an hour or more. My son lost interested in 10-15 minutes and it took a long time to get through books like the Narnia series. He didn't enjoy those books at all. I'd wait on the longer books if her attention span is pretty short. Stick to shorter chapter books that you can read in 3-4 sittings. Save the longer books for when she is a couple of years older.

"Have you Filled a Bucket" today is one of the first books that a lot of kindergarten classes read together. It talks about the concept of bucket fillers and bucket dippers and is an easy for kids to understand what it means to be a good friend. In my son's class room, the only rule this year was "Be a Bucket Filler" because it covered so many things.

The Junie B Jones books are great chapter books for that age. You can also try Charlotte's Web-- my son didn't like it, but a lot of his classmates did. You could also get something like the Katy Duck or Biscuit series (Alyssa Capucilli) and read a different one each evening.

Stop by your local library and talk to the children's librarian. They'll have lots of ideas.

Anything by Dr Seuss.
Chronicles of Narnia
The Hobbit
I focused on topics my son found interesting - so we read about sharks, dinosaurs, firetrucks, wizards, dragons, etc - they weren't focused specifically on friends/friendships but sometimes the concepts were there.
Harry Potter - first several books are great for younger readers and Harry, Ron and Hermione are great friends even if they argue from time to time.
The later books get a bit darker - save those for when she's older.
We started out with me reading a chapter a night as a bedtime story to him.
It got him more interested in reading chapter books himself.
I wanted our son to get so interested in the stories that he didn't care if it was a bit challenging to read - it really got him to stretch his reading muscles and he was reading beyond his age level by the 3rd grade - by 8th grade he was reading at college level.
Follow her interests and your daughters reading will take off.
I think recreational reading should be more about fun and less about 'lessons'.
Don't get me wrong - she'll learn plenty by reading - but she's got to enjoy it first.
My husband is surprised our son loves reading so much - it's not something Hubby ever really enjoyed - it was a chore for him,
Our son is heading to college in Aug - and he now points out books to me that he thinks I would enjoy reading.
I'm just so proud I've helped him find a joy that will be with him his whole life long.

We loved the Chicken Soul for the Kids Soul books. The stories are so touching and I really think these stories helped shape my daughter's into the empathetic kind people they are today. It also provided a great avenue for conversation about lots of topics.

Your local librarian is an invaluable resource for this question. Additionally, I like Usborne to look at age appropriate books (no, I do not sell them).

Yikes! Harry Potter at preK? That seems a bit "tiger mom" in my book. Plus, I feel like while listening comprehension can be high in some kids in that age group, chapter books that carry a story over a long period of time still seems quite advanced for a pre-k kiddo.

Check out storytime for pre-k at your local library and see what kids are actually reading/listening to (still shaking my head at a pre-k "reading" HP).

Good luck!