My older daughter is is an advanced reader, though she didn't hit her stride until 2nd grade.
Here is a list of books I have recommended for 1st-2nd graders to other parents and teachers.
Early Chapter Books
Princess Posey series
Heidi Hecklebeck series
Mermaid Tales series
Chapter Books
Cam Jansen series
Magic Tree House series
Box Car Children series
A to Z Mystery series
Nancy Drew and Clue Crew series
American Girl series
Clementine series
Ivy and Bean series
Marty McGuire series
Ramona series
Just Grace series
Never Girl series
Thea Stilton series
Like Pickle Juice on a Cookie - in verse, there are now 2 more books in the series.
Stella Batts series
Marty McGuire series
Toys Go Out/Toy Dance Party/Toys Come Home
Year of the Book - multicultural, Chinese-American, there are two more books in the series now.
Anna Hibiscus series - multicultural, takes place in Africa
The No 1 Car Spotter series - multicultural, takes place in Africa
Spiderwick Chronicles
The Trouble with Chickens - mystery, multiple POV
Stink series
The One and Only Stuey Lewis series
Invisible Inkling series
The Buddy Files series - mystery
Gone Fishing: a novel in verse