So you've finally gotten around to Heartless by Marissa Meyer (hey, me too!) and you loved it. Here's what to read next. For the record, this list assumes you have read Meyer's series Lunar Chronicles already. If you have not read it, then that is a great place to start. Same with the source material book: Alice in Wonderland by Lewis Carrol
You want more Alice in Wonderland retellings/reimagings:
The Looking Glass Wars Trilogy by Frank Beddor
Older Alice in Wonderland trilogy that imagines that in fact, Alice was a princess in Wonderland who cam to our world to escape bloodshed and then as a grown teen, goes back to take back wonderland. In other words: what I wish Tim Burton's Alice in Wonderland could have been.
Splintered series by A. G. Howard
I won't lie: this series has its issues, but this version of Wonderland is so imaginative that I sort of forgive the sigh-worthy tropes that abound in this series. The love triangle was also one of the few that doesn't force one guy under the bus in favor of another so that was a nice change. I still think they should have just ended in OT3...but alas, this is YA.
Did Lewis Carroll write anything else? (the answer is yes):
Jabberwocky and Other Nonsense: Collected Poems by Lewis Carroll
Along with Alice in Wonderland, Carroll wrote several poems, one of which whose titles you may recognize from Heartless...
You want to know more about Lewis Carroll:
Lewis Carroll: A Biography by Morten N. Cohen
The Mystery of Lewis Carroll: Discovering the Whimsical, Thoughtful, and Sometimes Lonely Man Who Created Alice in Wonderland by Jenny Woolf
Random things you may be interested in:
Alice, I Have Been by Melanie Benjamin
Great historical fiction book about the real girl who inspired the character of Alice. Also gives some good insight into Lewis Carroll.
Beware the Little White Rabbit by various authors
Short story collection that has several stories that give various nods to Alice in Wonderland
Alice in Verse: The Lost Rhymes of Wonderland by J. T. Holden
Poetry book that reimagines Alice in Wonderland
Twelve Impossible Things Before Breakfast by Jane Yolen
Short story collection that has at least one story referencing Alice in Wonderland.
The Search for Wondla series by Tony Diterlizzi
Middle-gradeish series that sort of borrows from Wonderland with beautiful illustrations throughout the book from the guy who illustrated The Spiderwick Chronicles series.